External frost stat is in action or not doing anything?

[Jurgenjay]

Hi,

I have an external frost stat which I am not sure if it is in use or not. I had an electrician opened it and checked it, he said it is live. But he is not sure if it is in action or not....
I took a photo, could anyone confirm as the position it is, is this frost stat in action i.e. will protect boiler if temperature drops to some degree? If yes, what temperature it is set?

Thank you!

 

[John.g]

Measure or estimate the ambient temperature at the stat then just turn the dial slowly clockwise or anti clockwise until you hear a click, then note what reference mark, if any the temp setting on the dial that's closest to your measured temperature. (there seems to be a reference mark opposite 20C on the dial but very unlikely its set to this).
It should be set to 5C IMO.

Ensure boiler off before turning it up to check if boiler restarts, surprising the electrician didn't do this.

 

[Jurgenjay]

Measure or estimate the ambient temperature at the stat then just turn the dial slowly clockwise or anti clockwise until you hear a click, then note what reference mark, if any the temp setting on the dial that's closest to your measured temperature. (there seems to be a reference mark opposite 20C on the dial but very unlikely its set to this).
It should be set to 5C IMO.

Ensure boiler off before turning it up to check if boiler restarts, surprising the electrician didn't do this.

Thank you! Last night this Forum was down & could not open anymore....
Did you try to show me how to set the frost protection temperature? I am not sure about it.
Yes, I heard it should be set to 5C.
From the photo, are you able to see what temperature it is set to?

 

[John.g]

No, I can't really see from the photo where it's set to, its set to ~ 20C, if the REFERENCE MARK is where I am showing it with the arrow but as I said this is unlikely and why I suggest getting a household thermometer and measuring the (garage) ambient temperature close to the frost stat, then turn the dial clockwise/anticlockwise slowly until you hear a click, post a photo again when you hear/identify this.

 

[Jurgenjay]

No, I can't really see from the photo where it's set to, its set to ~ 20C, if the REFERENCE MARK is where I am showing it with the arrow but as I said this is unlikely and why I suggest getting a household thermometer and measuring the (garage) ambient temperature close to the frost stat, then turn the dial clockwise/anticlockwise slowly until you hear a click, post a photo again when you hear/identify this.

Hi John, Thank you again for your reply!

I just checked and turned the dial anti-clockwise, when I heard the click I stopped and took the photo(the green line & question mark is what you meant REFERENCE MARK, right?)---attached photo1;
The photo 2 is the garage temperature I just measured for where the boiler and frost stat locate;
The photo 3 is the original (without turning) position----At this position you cannot turn the dial clockwise anymore, it is to the end & stuck there----can only turn anti-clockwise.
As you can see from photo 1 and photo3, the REFERENCE MARK position is different now.

Also, when I heard the click---as per photo1 position, the boiler started to fire, burner light (green light) was on, and blue light was on, I went upstairs to see the zone valve for hot water opened & the pump made noise!

But I heard the external frost stat normally is wired to heating not hot water? Is my system correct?

Thanks!

 

[Gasmk1]

The arrow should be straight up the defence in the lager tooth sharp at top behind dial

 

[Jurgenjay]

The arrow should be straight up the defence in the lager tooth sharp at top behind dial

Thank you!
Did you mean the arrow (above"5") position should be straight up like attached photo? I marked a down-arrow on the wall, so is that the line should the arrow on the stat face up to?

 

[John.g]

The arrow should be straight up the defence in the lager tooth sharp at top behind dial

The 12 oclock position would seem normal all right.
The measured temperature is 12.5C and (photo1) so a setting of 8.5C which closed the contactsmeans that the stat has a offset (hysteresis) of 4C, if this is correct then the stat should be set at "2" or where it originally was which will close the contacts at approx 5C??.

 

[John.g]

Thank you!
Did you mean the arrow (above"5") position should be straight up like attached photo? I marked a down-arrow on the wall, so is that the line should the arrow on the stat face up to?

Yes, more or less correct, but a setting of 8.5C equals to your measured temperature of 12.5C so maybe repeat your test and if the same I would set the stat almost fully clockwise to its original setting of "2" which means that the stat will operate when the temperature is 5C?.

 

[Jurgenjay]

The 12 oclock position would seem normal all right.
The measured temperature is 12.5C and (photo1) so a setting of 8.5C which closed the contactsmeans that the stat has a offset (hysteresis) of 4C, if this is correct then the stat should be set at "2" or where it originally was which will close the contacts at approx 5C??.

The arrow straight up---if this means 5C then the original position(photo3) it means 0C?
My installer's boss who told me the installer(had left the boss) said"he had disconnected the external frost stat", if so, then the original position(0C?) means the frost stat is not in use?
Until today I turned the dial anti-clockwise and heard the click---which is photo1 position: the boiler started to fire, zone valve for hot water opened, green and blue light were on.
So at photo 1 position, the frost stat is in action? ---but today the garage is 12.5C which is too high for frost protection temperature?

 

[Jurgenjay]

Yes, more or less correct, but a setting of 8.5C equals to your measured temperature of 12.5C so maybe repeat your test and if the same I would set the stat almost fully clockwise to its original setting of "2" which means that the stat will operate when the temperature is 5C?.

Hi John, please see my earlier reply.
almost fully clockwise"2"---it might meant by the installer that "was disconnected"?

 

[John.g]

No, not at all, it just means that the stat will operate theoretically when the garage temperature falls to 2C that the stat will operate, you can't turn off a stat. but because the stat operated at a setting of 8.5C when the actual measured temperature is 12.5C then a setting of 5C will (probably) mean that the stat will operate at 9C which is too high,so suggest setting it to 2C which means it will operate at a higer temperature of around 5/6C.

To ensure that it's connected correctly you might turn off the HW and CH zones and carry out your test again, it should then fire up the boiler again.

 

[Jurgenjay]

No, not at all, it just means that the stat will operate theoretically when the garage temperature falls to 2C that the stat will operate, you can't turn off a stat. but because the stat operated at a setting of 8.5C when the actual measured temperature is 12.5C then a setting of 5C will (probably) mean that the stat will operate at 9C which is too high,so suggest setting it to 2C which means it will operate at a higer temperature of around 5/6C.

To ensure that it's connected correctly you might turn off the HW and CH zones and carry out your test again, it should then fire up the boiler again.

Thanks for letting me know the stat cannot be turned off! The installer(left the job) told his boss he disconnected the frost stat which now seems a lie to his boss (his boss does not know it is connected or disconnected hence I am asking here)

"the stat operated at a setting of 8.5C"---This is just the position when it clicked today, right? If so, everyday it could be at different position? As everyday temperature can be different? e.g. cold or warm days.

When the click happened, the boiler started to fire, the zone valve for hot water opened, green and blue light were on.
How do I turn off the zone valves for HW and CH?

 

[John.g]

""the stat operated at a setting of 8.5C"---This is just the position when it clicked today, right? If so, everyday it could be at different position? As everyday temperature can be different? e.g. cold or warm days.
It doesn't matter what the garage temperature is, if you have the stat set to operate at 5C then the garage temperature will have to fall to 5C before the boiler fires up, when the temperature reaches ~ 8/9C, the boiler will stop firing. You deliberately increased the setpoint to test the stat operation only.
"
You should or may have HW and CH selections on your programmer where you can set the times that you want them off and on, something like this one.

 

[Jurgenjay]

""the stat operated at a setting of 8.5C"---This is just the position when it clicked today, right? If so, everyday it could be at different position? As everyday temperature can be different? e.g. cold or warm days.
It doesn't matter what the garage temperature is, if you have the stat set to operate at 5C then the garage temperature will have to fall to 5C before the boiler fires up, when the temperature reaches ~ 8/9C, the boiler will stop firing. You deliberately increased the setpoint to test the stat operation only.
"
You should or may have HW and CH selections on your programmer where you can set the times that you want them off and on, something like this one.

On thread #5, photo 3 that is what the original position, you said that was set as 2C, right?

But you said suggest setting it to 2C which means it will operate at a higher temperature of around 5/6C.===why set it at 2C & will operate at a higher temperature of around 5/6C?
Why there's 4C difference?

I have the attached programmer, is this what you meant? I use this to set the timing for HW and CH start and finish time.

Thank you!

 

[John.g]

There is a difference of 4C because you discovered that yourself when the stat operated at a setting of 8.5C when the actual measured temperature was 12.5C , (12.5-8.5 = 4). All thermostats will have some difference between the setting temperature and the measured temperature, 4C might be a bit on the high side but you can compensate by making the setpoint 4C lower, in this case if you require the stat to operate at 5/6C you set it to 2C (6-4 = 2).

Re programmer, yes, that's it, so if you ensure both CH and HW Off then the boiler should still fire when you test it by increasing the frost stat setting until it clicks on. After testing, return it again to 2C.

 

[Jurgenjay]

There is a difference of 4C because you discovered that yourself when the stat operated at a setting of 8.5C when the actual measured temperature was 12.5C , (12.5-8.5 = 4). All thermostats will have some difference between the setting temperature and the measured temperature, 4C might be a bit on the high side but you can compensate by making the setpoint 4C lower, in this case if you require the stat to operate at 5/6C you set it to 2C (6-4 = 2).

Re programmer, yes, that's it, so if you ensure both CH and HW Off then the boiler should still fire when you test it by increasing the frost stat setting until it clicks on. After testing, return it again to 2C.

Yes, this afternoon I turned the dial anti-clockwise and when heard the click, I stopped, so the photo1 is the position as it was: 8.5C: the boiler started to fire, zone valve for hot water opened, green and blue light were on.
You mean to do this test again to obtain another setting temperature setting C or for what to do another test?
After testing, I turn it back to full clockwise i.e. 2C?

When you said setting frost stat at 2C, i.e. roughly the ambient temperature is 6C----this looks making sense for the case happened on 21st of January which the morning at 8:35am outside temperature was -6°C, and the garage (where my boiler is locates) temperature was 6.6°C, at the time, my boiler started to fire (outside of programmer setting period), zone valve for hot water opened, this lasted nearly 4 hours till 12:15pm.
So all this could be caused by the external frost stat triggered the boiler to start the frost protection function, right?

 

[John.g]

Don't think you need to repeat the test as the boiler fired up outside the programmed times so OK. The problem with this type of frost stat is that it is measuring a "room" temperature, ie the garage which is only heated by any radiated heat loss from the boiler so takes hours to reach the frost stat cut out temp which can be 4 to 6C higher than its setpoint.
If you were/are quite happy with the boiler itself which monitors the water temperatures and will only fire for the very minimum time required to prevent the water freezing, then all that probably has to be done to disable the external frost stat is to remove one wire in the stat.

You had another thread where it showed the parameters for the internal frost protection which seemed perfect.

I would suggest getting back on to the "boss" and tell him that the external stat is not disconnected.

 

[John.g]

You said.....
Below is the manual of my boiler regarding Frost Protection：

"If the temperature within the boiler falls below 8°C the pump will run to circulate water and prevent the system freezing. If the temperature within the boiler falls below 5°C the boiler will fire periodically, bringing the boiler temperature up to 12°C to avoid the possibility of the system freezing. This process will be repeated until such time that the boiler temperature does not drop below 5°C."

This is the full explanation of the above.

If the temperature within the appliance falls below 8°C the pump will run to circulate water and prevent the system freezing. – If the temperature does not rise to 9°C within 30 minutes of the pump operating, the appliance will fire up. ▶ If the temperature within the appliance falls below 5°C the appliance will fire immediately, bringing the appliance temperature up to 12°C to avoid the possibility of the appliance freezing. ▶ This process will be repeated until such time that the appliance temperature does not drop below 8°C."

 

[Jurgenjay]

Don't think you need to repeat the test as the boiler fired up outside the programmed times so OK. The problem with this type of frost stat is that it is measuring a "room" temperature, ie the garage which is only heated by any radiated heat loss from the boiler so takes hours to reach the frost stat cut out temp which can be 4 to 6C higher than its setpoint.
If you were/are quite happy with the boiler itself which monitors the water temperatures and will only fire for the very minimum time required to prevent the water freezing, then all that probably has to be done to disable the external frost stat is to remove one wire in the stat.

You had another thread where it showed the parameters for the internal frost protection which seemed perfect.

I would suggest getting back on to the "boss" and tell him that the external stat is not disconnected.

Hi John,
Thank you so much for your input throughout this thread! I got more useful information from you---on this website forum!
I should got all those answers from the gas engineer boss/team as they installed the boiler and all system, but the boss did not know the boiler/built-in frost protection/external frost stat/ zone valves how they work/should work etc. which forced me had to ask online! What a sad thing.....

As you suggested, I may need to get the external frost stat disconnected as it may conflict with the built-in frost protection?
I don't know how other houses do when they install a new boiler system i.e. get rid of the old external frost stat as nowadays new boiler normally has built-in frost protection already?

 

[Jurgenjay]

You said.....
Below is the manual of my boiler regarding Frost Protection：

"If the temperature within the boiler falls below 8°C the pump will run to circulate water and prevent the system freezing. If the temperature within the boiler falls below 5°C the boiler will fire periodically, bringing the boiler temperature up to 12°C to avoid the possibility of the system freezing. This process will be repeated until such time that the boiler temperature does not drop below 5°C."

This is the full explanation of the above.

If the temperature within the appliance falls below 8°C the pump will run to circulate water and prevent the system freezing. – If the temperature does not rise to 9°C within 30 minutes of the pump operating, the appliance will fire up. ▶ If the temperature within the appliance falls below 5°C the appliance will fire immediately, bringing the appliance temperature up to 12°C to avoid the possibility of the appliance freezing. ▶ This process will be repeated until such time that the appliance temperature does not drop below 8°C."

Thank you again John!
i am a bit curious that the way of the built-in frost protection function seems never in action...
In middle of Jan, especially on 21st of Jan (outside -6°C ) which were cold and minus 0°C, but I never noticed the pump circulating or boiler started fire. I measured on 21st of Jan the garage temperature was 6.6 °C---maybe the boiler water temperature was still higher than 8 °C thus frost protection still not in action?

As mentioned earlier, on 21st of January in the morning at 8:35am outside temperature was -6°C, and the garage (where my boiler is locates) temperature was 6.6°C, at the time, my boiler started to fire (outside of programmer setting period), zone valve for hot water opened, this lasted nearly 4 hours till 12:15pm.
All this could be caused by the external frost stat triggered the boiler to start the frost protection function, right?
So it seems external frost stat worked(not sure yet)? But built-in frost protection not?

 

[John.g]

The internal frost protection will only operate if the boiler water temperature falls below 8C (that's my interpretation of "the temperature within the appliance") so if the boiler was programmed on until say 2200 hrs each night then the boiler water temperature may well be ~ 50/55C at shutdown and it will take it a long time to fall to 8C, it may take more time to do this than the interval between night shut down and next morning start time, if so, then the external stat will have operated as its measuring the garage air temperature and it has fallen to ~ 6/7C.
You could look at the boiler water temperature a few times (if available on the boiler menu) during the next cold night and compare it with the garage temperature.
Remember, on Jan21st, the outside temperature was -6.0C and the garage temperature was +6.6C so the external frost stat operated more or less which now know will happen with a setting of ~ 2C (due to the 4C offset) and there is no way IMO that the boiler water temperature would have fallen to 8C (from 50/55C) during that period.

For interest, was the HW very hot that morning as the HW zone valve is opened during external frost protection period(s), I would have expected it to reach the boiler water cut out temp of 70C or whatever you have it set to.

 

[Jurgenjay]

The internal frost protection will only operate if the boiler water temperature falls below 8C (that's my interpretation of "the temperature within the appliance") so if the boiler was programmed on until say 2200 hrs each night then the boiler water temperature may well be ~ 50/55C at shutdown and it will take it a long time to fall to 8C, it may take more time to do this than the interval between night shut down and next morning start time, if so, then the external stat will have operated as its measuring the garage air temperature and it has fallen to ~ 6/7C.
You could look at the boiler water temperature a few times (if available on the boiler menu) during the next cold night and compare it with the garage temperature.
Remember, on Jan21st, the outside temperature was -6.0C and the garage temperature was +6.6C so the external frost stat operated more or less which now know will happen with a setting of ~ 2C (due to the 4C offset) and there is no way IMO that the boiler water temperature would have fallen to 8C (from 50/55C) during that period.

For interest, was the HW very hot that morning as the HW zone valve is opened during external frost protection period(s), I would have expected it to reach the boiler water cut out temp of 70C or whatever you have it set to.

Thanks a lot again John!
Your analysis regarding how the built-in frost protection works and external frost stat works look very reasonable!
This can explains why I never seen internal frost protection worked as you said, the boiler water temperature will take a long time to drop below 8C.
For that coldest day--21st of Jan (I tracked the temperature those days) in the morning 8:35am, the boiler started to fire, should be because the garage temperature dropped at around 6.6C---this should trigger the external frost stat to demand boiler to fire. And until the garage air temperature reached 7.5C(I measured at the time) the boiler stopped firing and zone valve closed.

You are right again for the HW! I did not check that day(21st of Jan) morning HW temperature, but I did have a shower right after the HW programmer was on a long time, I could feel HW was very hot!

 

[SJB060685]

I haven’t read every above comment so forgive me if this has already been mentioned.
The idea of a frost stat is as you know to prevent water in the boiler/system from reaching freezing point. The problem is as John mentioned above the garage will take quite some time to satisfy the frost stat on cold days because the only energy heating that air space is standing heat losses from the boiler. Boilers have both a combustion efficiency and an appliance efficiency. If the standing heat losses from your boiler are low then it would take hours, maybe even never satisfy the frost stat on cold days due to the garage having high heat loss itself.
Now the frost stat should be wired in series with a clamp on low temperature pipe stat on the return to the boiler, which SHOULD open the CH zone valve to dump the heat. The return clamp on stat is usually set to about 20°c and when the return water reaches that temperature the stat contacts will open and cut power to the CH valve and in turn the boiler. Without this additional clamp on stat you will get constant cycling at the burner.
Remember the idea of this setup is to prevent the boiler from freezing, while using as little fuel as possible.

 

[Jurgenjay]

I haven’t read every above comment so forgive me if this has already been mentioned.
The idea of a frost stat is as you know to prevent water in the boiler/system from reaching freezing point. The problem is as John mentioned above the garage will take quite some time to satisfy the frost stat on cold days because the only energy heating that air space is standing heat losses from the boiler. Boilers have both a combustion efficiency and an appliance efficiency. If the standing heat losses from your boiler are low then it would take hours, maybe even never satisfy the frost stat on cold days due to the garage having high heat loss itself.
Now the frost stat should be wired in series with a clamp on low temperature pipe stat on the return to the boiler, which SHOULD open the CH zone valve to dump the heat. The return clamp on stat is usually set to about 20°c and when the return water reaches that temperature the stat contacts will open and cut power to the CH valve and in turn the boiler. Without this additional clamp on stat you will get constant cycling at the burner.
Remember the idea of this setup is to prevent the boiler from freezing, while using as little fuel as possible.

Thanks for your input!
The first part I now understand it & it explains on 21st of Jan(coldest day of those minus degree days) morning why my boiler stated to fire outside of programmer setting period and lasted nearly 4 hours!

The second part, there maybe another issue from my newly installed system: it seems my external frost stat is wired in series with HW instead of CH! i.e. on the morning of 21st of Jan, when the boiler fired, the zone valve for HW opened NOT zone valve for CH!

The pipe stat is like attached photos?

Also, now, another issue I don't know whether it is same for zone valve for HW: even if when HW programmer is on for a long time, say a few hours, the zone valve for HW never close! and the blue light always on! The burner light (green light) is off, then on, then off for every a couple of minutes.

 

[SJB060685]

A clamp on stat is more like the image furthest to the left.
The HW zone valve should close when the cylinder stat is satisfied. If the motorised valve isn’t closing it’s still getting a feed from somewhere. It could be a faulty cylinder stat or the cylinder stat isn’t connecting properly with the cylinder if it’s an open vented HW system?

 

[Jurgenjay]

A clamp on stat is more like the image furthest to the left.
The HW zone valve should close when the cylinder stat is satisfied. If the motorised valve isn’t closing it’s still getting a feed from somewhere. It could be a faulty cylinder stat or the cylinder stat isn’t connecting properly with the cylinder if it’s an open vented HW system?

Yes, I also learned that the zone valve for HW and zone valve for CH should both close if the cylinder stat and house setting temperature are satisfied, but only zone valve for CH closed when it reaches house setting temperature, but zone valve for HW NEVER close during programmer "on" period (when programmer setting time is off, then the zone valve for HW does close---so it this looks zone valve is no problem, right?)
My system is unvented cylinder system.

 

[John.g]

Does the HW zone valve close when HW programmed off?. if so maybe something as simple as the boiler temperature not set 5 to 10C higher than the cylinder stat, ie if cylinder stat set to 60C, boiler should be set to 65/70C.

 

[SJB060685]

It could be wired wrong, it could be a dodgy stat or not sitting on cylinder properly. A photo of the cylinder and stat would help.
John raises a good point as well. If the cylinder stat is set to 60°c then the boiler flow should be higher.

 

[Jurgenjay]

Does the HW zone valve close when HW programmed off?. if so maybe something as simple as the boiler temperature not set 5 to 10C higher than the cylinder stat, ie if cylinder stat set to 60C, boiler should be set to 65/70C.

HW zone valve indeed close when HW programmer is off.
But your comment does draw my attention: "the boiler temperature not set 5 to 10C higher than the cylinder stat, ie if cylinder stat set to 60C, boiler should be set to 65/70C."
Is this a must? Could you explain this theory?
I just checked my temperature settings:
Please see photo1 which is my boiler photo, that is central heating setting, right? according to photo 2 "setting temperature for your heating", I turned the knob to the position around 5 which is 74C;
My cylinder stat is set to close to 65C, maybe 60C, or 61C, or 62C, please see photo 3.
So based on your theory, my central heating temperature(74C) and cylinder stat temperature(60,1,2C) are correct?

 

[Jurgenjay]

It could be wired wrong, it could be a dodgy stat or not sitting on cylinder properly. A photo of the cylinder and stat would help.
John raises a good point as well. If the cylinder stat is set to 60°c then the boiler flow should be higher.

Please see attached photo of stat on cylinder and cylinder, if they are good to judge?
Please refer to my last reply to John that how I set the cylinder temperature and boiler heating temperature.

 

[SJB060685]

The theory revolves around the first law of thermodynamics. Basically if the water leaving your boiler is max 60°c then the maximum temperature the water in the cylinder could ever be is 60°c. You have the cylinder stat at 65°c which in my opinion is 5°c too high because if you’re in a hard water area this temperature can cause lime scale to form. Set the cylinder stat to 60°c and leave the boiler at about 70°c. Any higher and you start to lose any condensing

 

[John.g]

The divisions on the cylinder stat are extraordinary at 6.66C/division just to create more of a challenge when setting it?.

Anyway, to test the stat, just turn it down and see if the HW cylinder zone valve closes while programmed on.

 

[Jurgenjay]

The theory revolves around the first law of thermodynamics. Basically if the water leaving your boiler is max 60°c then the maximum temperature the water in the cylinder could ever be is 60°c. You have the cylinder stat at 65°c which in my opinion is 5°c too high because if you’re in a hard water area this temperature can cause lime scale to form. Set the cylinder stat to 60°c and leave the boiler at about 70°c. Any higher and you start to lose any condensing

Thank you for letting me know this theory!
My cylinder stat is not set as 65°c, it is about 60-65°c. It is because between 65°c---45°c the gap is 20°c, there are 3 gaps, so i set it between 65°c and the next mark.
The reason I set on that position (60-65°c )is because I learned that the hot water should be set over 60°c in order to kill legionella bacteria. (as attached picture)
So for my cylinder stat temperature, I should/could turn the heating setting knob smaller, say between 4-5 to make it around 71°c ?(this attached photo2)

 

[John.g]

That sound correct Jurgen but to check correct wiring, you might do the test I suggested in post #33.