mid position valve faulty?

[drollord]

I have a problem that occurs about once a month.

I run the HW and CH set on continuously 24/7, using the room stat to control CH and the tank stat fixed at 60°c for HW.

The HW and CH sometimes refuse to switch off when their respective temperatures are are reached which results in excessively
hot HW and continual heating of radiators when not needed.

There is no response from the room stat, the tank stat and the heating control panel will not switch off or change settings.
The usual remedy was to pull the mains plug from the wall socket which reset everything and off we would go for another few
weeks with everything working fine.

Anyway, I have been doing some investigation since the last occurence and the one that has just happened.
It appears I have a faulty mid position valve (its an Iflo, looks exactly like a Drayton). The mechanical valve in the
pipework is very free moving, it is the electrical box part that is the problem. Under normal working the black switch
moves from HW to CH or mid postion and moves inwards to lock out in the CH and mid position. While this was functioning
correctly I took some voltage readings on the wiring centre (junction box) and then waited until the fault occured and took
readings again. Terminal 7 showed 130v where it should have been zero (readings attached).

Upon finding the fault the black switch was in the CH position but NOT locked out, so the switch could be moved quite easily
by hand. Moving the switch by hand had no effect of turning the HW or CH off. I took the valve box off the pipework and
gave it a shake which then made the switch go to the CH position and lock out, turning off the CH and HW in the process.
What I do not know is, does the synchronous motor need replacing or the whole of the top part with the rest of the electrics
in it.

Anyone had a similar experience or be prepared to comment?
many thanks
mick

 

[diamondgas]

I'd check the movement of the valve spindle, see if it's free or stiff. If free then I's replace the whole of the actuator mick. Sounds like one of the switches is sticking ...... 130v is not uncommon and doesn't indicate any fault by the way here's a handy link UK DIY FAQ

 

[drollord]

I'd check the movement of the valve spindle, see if it's free or stiff. If free then I's replace the whole of the actuator mick. Sounds like one of the switches is sticking ...... 130v is not uncommon and doesn't indicate any fault by the way here's a handy link UK DIY FAQ

The valve spindle is fine, I can move it with my thumb/finger.

 

[R1CKY]

Had this happens with a drayton 2 port valve on more than one occassion. Microswitch was getting stuck in the closed position, so valve would close, boiler would continue to heat and eventually over heat. I'd imagine the microswitches are the same in the three port too, so could well be the cause.

 

[drollord]

Had this happens with a drayton 2 port valve on more than one occassion. Microswitch was getting stuck in the closed position, so valve would close, boiler would continue to heat and eventually over heat. I'd imagine the microswitches are the same in the three port too, so could well be the cause.

Thanks Ricky, I am sure you are 99% correct. The switches are the last mechanical device that move in the head. The motor seems good as it operates normally and resets itself to the correct position when I pull the mains supply. Unfortunately I cannot see the micro switches operating when the head is in position as they are hidden under the motor plate and I am not keen to have the head all opened up with mains supply still live then go poking about with a screwdriver:angelsad2: Anyway, they are soldered to the circuit board so it is not easy to exchange. Looks like a new head and keep the old one for spares:smile:


mick

 

[doitmyself]

According to the table of voltages there is 0 volts on terminal 5 when the fault occurs. This should be 240V coming from the room thermostat and feeding the valve white wire. So either the room stat is faulty or the CH On channel of the programmer is faulty.

Disconnect the white wire (to prevent voltage feed back) and check voltage on terminal 4 (CH ON) when programmer has heating on; it should be 240V. Check with the various options on the programmer - ON, timed - as it may be a clock fault not turning the heating on..

If this is OK, check terminal 5 (0V when stat turned down; 240V when stat turned up).

 

[drollord]

According to the table of voltages there is 0 volts on terminal 5 when the fault occurs. This should be 240V coming from the room thermostat and feeding the valve white wire. So either the room stat is faulty or the CH On channel of the programmer is faulty.

Disconnect the white wire (to prevent voltage feed back) and check voltage on terminal 4 (CH ON) when programmer has heating on; it should be 240V. Check with the various options on the programmer - ON, timed - as it may be a clock fault not turning the heating on..

If this is OK, check terminal 5 (0V when stat turned down; 240V when stat turned up).

Just checked with the system working ok. All the programmer settings are showing 225V at terminal 4, and room stat is showing 0V and 225V

I was just wondering from Ricky's post where we suggested faulty limit switches if I could physically reproduce the fault by removing one or other wire that connects to the limit switches. I am assuming they are the grey and blue wires from the valve.

 

[diamondgas]

Just checked with the system working ok. All the programmer settings are showing 225V at terminal 4, and room stat is showing 0V and 225V

I was just wondering from Ricky's post where we suggested faulty limit switches if I could physically reproduce the fault by removing one or other wire that connects to the limit switches. I am assuming they are the grey and blue wires from the valve.

2port works differently to a 3port valve Mick. Only one switch and the motor is either powered or dead!

 

[doitmyself]

Just checked with the system working ok. All the programmer settings are showing 225V at terminal 4, and room stat is showing 0V and 225V

No point checking when it's working correctly! You have to check when it is faulty. You are trying to find out why there is 0v on terminal 4 when there should be 225-240V. It will be either a faulty programmer or a faulty stat; nothing to do with the valve.

Did you disconnect the white wire when measuring the voltage at T4?

 

[drollord]

No point checking when it's working correctly! You have to check when it is faulty. You are trying to find out why there is 0v on terminal 4 when there should be 225-240V. It will be either a faulty programmer or a faulty stat; nothing to do with the valve.

Did you disconnect the white wire when measuring the voltage at T4?

I have to wait for the fault to happen which could be hours or days or in the last instance it was five weeks!:yawn:

I did disconnect the white wire as you said.

Last time the fault occurred I just took the head off and gave it a shake, as the head was still in my hand the lever moved the CH position and locked out, the boiler then shut down because then temperature on both stats had reached (gone beyond) their set temperatures. Thats why I tended to agree with Ricky who said it could be the one or both of the micro switches sticking.

My only concern is disconnecting the white wire whilst it may be live to check the voltages. If I switch off the mains first, disconnect the wire then restore mains supply that resets everything back to normal and therefore I would not get a reading in the faulty state.

 

[lame plumber]

not being smart bum but why leave heating on 24/7 leave it turned down overnight and youll save money, and pay for a new head in no time.

 

[doitmyself]

I take your point about turning off the power will reset the valve. However, I have checked the internal circuitry and there will not be any feedback on the white wire, so no need to disconnect.

I am not convinced that it is a fault with the micro-switches as they cannot cause the lack of voltage on terminal 5.

So, that leaves the questions:

1. Why is there 0V on the white wire when there should be 240V?

2. Does this happen every time the fault occurs?

 

[drollord]

I take your point about turning off the power will reset the valve. However, I have checked the internal circuitry and there will not be any feedback on the white wire, so no need to disconnect.

I am not convinced that it is a fault with the micro-switches as they cannot cause the lack of voltage on terminal 5.

So, that leaves the questions:

1. Why is there 0V on the white wire when there should be 240V?

2. Does this happen every time the fault occurs?

I have only checked the voltages once, the last time that the system locked up. I am still waiting for the next occurance of the fault.

If there is no voltage at 5 then that means the CH and HW are not calling for heat, YET the boiler is still going, give the head a shake then the lever on the head goes from a 'floppy state' (can manually move it anywhere and nothing happens) to the CH position and locks out, the boiler then shuts down.

 

[drollord]

not being smart bum but why leave heating on 24/7 leave it turned down overnight and youll save money, and pay for a new head in no time.

The heating is turned down overnight by usuing the room stat, usually to about 18°C. Very, very rarely does the heating ever come on overnight unless exceptionally cold. -9°C last week and still did not come on overnight. They key is a well insulated house.

 

[doitmyself]

If there is no voltage at 5 then that means the CH and HW are not calling for heat,

That's not correct.

Terminal 5 is fed from the CH ON terminal of the programmer via the room stat. It has nothing to do with the HW side.

Going back to your first post you said:

The HW and CH sometimes refuse to switch off when their respective temperatures are are reached which results in excessively hot HW and continual heating of radiators when not needed.

There is no response from the room stat, the tank stat and the heating control panel will not switch off or change settings.

Are you talking about just CH or HW not turning off, or when both are turned off?

It might be worth experimenting, using the room and cylinder stats, to determine exactly when the problem occurs.

You can forget about the 0 volts on terminal 5, this is quite correct when the heating is turned off by the room stat. The problem is on the HW side: why is there 240V on T6 and T8, and 130V on T7?

 

[secret squirrel]

I haven't read all the posts had too much to drink! if your sure the valve is faulty change the whole thing. if your doing the job yourself change it all anyway, it'll only cost the valve and some inhibitor, job done!

 

[newagegasman]

Those type of heads on the three port valves are always palying up.. i change them yearly. but anyway call somebody competent in.

 

[drollord]

That's not correct.

Terminal 5 is fed from the CH ON terminal of the programmer via the room stat. It has nothing to do with the HW side.

Going back to your first post you said:


Are you talking about just CH or HW not turning off, or when both are turned off?

It might be worth experimenting, using the room and cylinder stats, to determine exactly when the problem occurs.

You can forget about the 0 volts on terminal 5, this is quite correct when the heating is turned off by the room stat. The problem is on the HW side: why is there 240V on T6 and T8, and 130V on T7?

When the fault occurs, turning both stats to their minimum settings does not turn off the boiler.

As of this very moment the room stat is at 24°C and the HW stat at 60°C. If I turn up both stats there is an audible click at both stats. 24°C is comfortable, if it goes above that I notice very quickly the rise in temperature, also if the HW rises to 70°C it becomes unbearable through the taps. The maximun setting on the room stat is 30°C and the HW is 80°C. When the fault occured I am certain the room temperature was less than 30, but I could not say what the HW temperature was. Turning the stats up or down when the fault occured there was no audible click from either stat.

T6 and T8
In the fault condition 225V at T8 indicates(to me) that the lever on the head should be in the CH position. It was however in the mid postion, but I could move it by hand to any position and it had no effect on shutting the boiler down. As to T7, I am mystified.

From all the posts I have built up a check list of what to do and in what order next time I get this fault. The problem doesn't bother me as I know I can just go and buy a new head or whatever else but I would like to know exactly what it is and it could be of help to other people.
Thanks for your patience
mick

 

[doitmyself]

T6 and T8
In the fault condition 225V at T8 indicates(to me) that the lever on the head should be in the CH position. It was however in the mid postion, but I could move it by hand to any position and it had no effect on shutting the boiler down. As to T7, I am mystified.

I've sussed out the T6/T8 problem: there isn't one!

T6 is fed from programmer HW ON, so there will always be 240V on it as you never turn the HW off at the programmer.
T8 will have 0V when the cylinder stat is calling for heat and 240V (from T6) when the cylinder is satisfied.

As for the 130v on T7, this is perfectly normal. When the valve has been in the CH only position and CH is satisfied (room stat turns off) or turned off by the programmer, there will be 0V on the white and 230V on the grey. The valve stays in the CH only position and one of the internal switches connects grey to orange via a resistor, which drops the voltage from 240V to approx 150V. In normal circumstances this is not enough to light the boiler, but there have been cases where it can light the boiler. Which boiler do you have (make and model).

You may find How a mid-position valve works helpful.

 

[drollord]

I've sussed out the T6/T8 problem: there isn't one!

T6 is fed from programmer HW ON, so there will always be 240V on it as you never turn the HW off at the programmer.
T8 will have 0V when the cylinder stat is calling for heat and 240V (from T6) when the cylinder is satisfied.

As for the 130v on T7, this is perfectly normal. When the valve has been in the CH only position and CH is satisfied (room stat turns off) or turned off by the programmer, there will be 0V on the white and 230V on the grey. The valve stays in the CH only position and one of the internal switches connects grey to orange via a resistor, which drops the voltage from 240V to approx 150V. In normal circumstances this is not enough to light the boiler, but there have been cases where it can light the boiler. Which boiler do you have (make and model).

You may find How a mid-position valve works helpful.

Thanks for the link.
The boiler is a Worcester Greenstar 18Ri

mick.

 

[doitmyself]

The boiler is a Worcester Greenstar 18Ri.

I believe that is one of the boilers which will run when there is 150V or so on the orange.

You will only get this problem if the valve is in CH only position when the heating turns off.

Here's a quick way of checking if that is the cause:

With programmer set to CH ON and HW ON

1. Turn room stat and boiler stat up
The valve should go to mid-position; boiler should light and rads & cylinder warm up
2. Turn room stat down
The valve should go to HW only;boiler should continue to run.
3. Turn cylinder stat down
Valve should stay in HW position; boiler should stop.
4. Turn cylinder stat up then turn room stat up
Valve should go to mid-position; boiler runs; rad and cylinder heats up.
5. Turn cylinder stat down
Valve goes to CH position; boiler runs; rads only heat up.
6. Turn Room stat down
Valve should stay in CH position; boiler should stop.

If the boiler does not stop, it's because the voltage on the orange wire is enough to turn on the gas valve.

 

[drollord]

I believe that is one of the boilers which will run when there is 150V or so on the orange.

You will only get this problem if the valve is in CH only position when the heating turns off.

Here's a quick way of checking if that is the cause:

With programmer set to CH ON and HW ON

1. Turn room stat and boiler stat up
The valve should go to mid-position; boiler should light and rads & cylinder warm up
2. Turn room stat down
The valve should go to HW only;boiler should continue to run.
3. Turn cylinder stat down
Valve should stay in HW position; boiler should stop.
4. Turn cylinder stat up then turn room stat up
Valve should go to mid-position; boiler runs; rad and cylinder heats up.
5. Turn cylinder stat down
Valve goes to CH position; boiler runs; rads only heat up.
6. Turn Room stat down
Valve should stay in CH position; boiler should stop.

If the boiler does not stop, it's because the voltage on the orange wire is enough to turn on the gas valve.

BINGO! you have recreated my fault.

I went through your sequence and noted the voltage at T7(orange wire)

I. system OK, 225v
2. system OK, 225v
3. system OK, 0v
4. system ok, 225v
5. valve stayed in mid position, 130v
6. valve still in mid position, 225v
Boiler would not shut down

Pulled mains supply and reconnected, valve gone HW position, boiler not fired up as its like a sauna in here!

mick

 

[drollord]

BINGO! you have recreated my fault.

I went through your sequence and noted the voltage at T7(orange wire)

I. system OK, 225v
2. system OK, 225v
3. system OK, 0v
4. system ok, 225v
5. valve stayed in mid position, 130v
6. valve still in mid position, 225v
Boiler would not shut down

Pulled mains supply and reconnected, valve gone HW position, boiler not fired up as its like a sauna in here!

mick

DAMN!

I have tried the sequence a couple more times and cannot get it to replicate the fault again.
Will have another go tomorrow when its cooled down a bit more.
mick

 

[doitmyself]

BINGO! you have recreated my fault.

I went through your sequence and noted the voltage at T7(orange wire)

5. valve stayed in mid position, 130v
6. valve still in mid position, 225v
Boiler would not shut down

What makes you say that the valve stays in mid-position?

 

[drollord]

I have started from from scratch today.
Both stats at zero, boiler off and valve in HW position.
I have had someone help to turn the stats while I have watched the valve movement and noted the voltages.
We have gone through the 1-6 proceedure four seperate times over about 3 hours and nothing has gone wrong, the valve movement has been correct in every case. The boiler fired up and shut down as it should.
When it went wrong last night at stage 5, the valve remained at the mid position and T7 had 130v.
Could it be tank stat at fault and/or sticky microswitches in valve head.

voltages taken today at each stage.

	T 4	T5	T6	T7	T8
1	225	225	225	225	90
2	225	0	225	225	90
3	225	0	225	0	225
4	225	225	225	225	90
5	225	225	225	225	225
6	225	0	225	0	225

 

[doitmyself]

voltages taken today at each stage.

	T 4	T5	T6	T7	T8
1	225	225	225	225	90
2	225	0	225	225	90
3	225	0	225	0	225
4	225	225	225	225	90
5	225	225	225	225	225
6	225	0	225	0	225

All the voltages are OK except those in colour. I'm not sure about the 90 volt readings, they could be a quirk of the valve, but the 225 volt reading on T7 at stage 5 is definitely wrong; it should be 0 volts.

Disconnect all wires from T7 and T8 except those to the cylinder stat

Turn stat to Minimum: You should get 0 on T7 and 225 on T8
Turn stat to Maximum: You should get 225 on T7 and 0 on T8

Check this several times. It might be worth checking to see if there is a point between max and min where you get 225v on both T7 and T8 - there shouldn't be one!

If you don't get the correct readings, the cylinder stat is faulty.

 

[drollord]

All the voltages are OK except those in colour. I'm not sure about the 90 volt readings, they could be a quirk of the valve, but the 225 volt reading on T7 at stage 5 is definitely wrong; it should be 0 volts.

Disconnect all wires from T7 and T8 except those to the cylinder stat

Turn stat to Minimum: You should get 0 on T7 and 225 on T8
Turn stat to Maximum: You should get 225 on T7 and 0 on T8

Check this several times. It might be worth checking to see if there is a point between max and min where you get 225v on both T7 and T8 - there shouldn't be one!

If you don't get the correct readings, the cylinder stat is faulty.

Have done what you said.
at minimum T7 60v T8 225v
at maximum T7 225v T8 60v
there is no point where both T7 and T8 are at 225v
the change over happens at the point of tank temperature which at the moment is 60° and an audible click of the stat is heard
Where's this 60v reading come from?

 

[doitmyself]

Have done what you said.
at minimum T7 60v T8 225v
at maximum T7 225v T8 60v
there is no point where both T7 and T8 are at 225v

Did you disconnect all wires, except those from the cylinder stat, from T7 and T8?

 

[drollord]

Did you disconnect all wires, except those from the cylinder stat, from T7 and T8?

Yes, most definately!

 

[doitmyself]

Yes, most definitely!

Then the cylinder stat is knackered!