Pump overrun is killing my heating!

[John.g]

"I would advise to remove the VR40 and wire the single system pump as shown in the example diagram below with a permanent 230V supply to the grey wires and use the oranges from all zone valves wired to the pump live."

That is the normal S plan configuration, there is a permanent live to one side of the zone valve end switches and all the wires (switched live) from the other end(s) are marshalled together to provide a a run signal to the boiler which now normally controls the boiler circ pump, so if any one, or all, zone valves are open then the boiler has a run signal and when all zone vales are shut then no run signal, I suppose with all their fancy control systems now, they don't use the end switches now but employ some virtual means of determining this hence all these status alerts or whatever.
It's a bit surprising that there is no contact on the boiler from the circ pump run signal, there must be some means of picking up this and wiring it via a external relay (if required) to run the external pump, I think this was suggested previously, above. Also, this implies that the (a) zone valve is kept open for the duration of any pump overrun, oh no, the pump won't run unless a zone valve is open!.

 

[milleniumaire]

Got up early this morning, prior to the heating/hot water turning on at 6:30am, so I could monitor temperatures etc.

Took readings before the boiler started up. This showed the current cylinder temperature was 56 deg C (the desired setting is 60). So, 4 deg C heat loss over 7.5 hours, which seems much better than the other night

When the boiler started up it went straight into heating mode, I guess because 56 is within 5 of 60, so no need to heat up the cylinder.

Had a shower then re-checked at 06:55 and the boiler was now heating up the cylinder, which it did within about 10 mins as by 7:10 it was back to heating mode.

So, everything worked perfectly, even the shower controls! Had a chat with my son and he admitted he had been having late night showers every 2 or 3 days!!!!!! If only I had known that.

It would therefore appear that a combination of the cylinder temp being set to 65 and my son's late night, secret showers using up hot water are possibly the reasons for the cylinder taking so long to heat up in the morning.

Obviously, there are still settings to change and possibly wiring to change, or at least an explanation of the wiring settings, so I await feedback from Vaillant, but it would appear the "pump overrun" situation I thought was occurring is a red herring! I'll update when I hear from Vaillant.

 

[John.g]

It would b interesting during the day to run off some hot water until the system changes over to HW, then stop running off the hot water and monitor the exact time taken to reach cut off at 60C, also a full set of readings during its run including cylinder top and target temperatures, LLH temperatures etc, can then tell pretty exactly the performance of the cylinder "coil" and might then be able to understand why it should take so long to reach 65C, if required.

 

[milleniumaire]

It would b interesting during the day to run off some hot water until the system changes over to HW, then stop running off the hot water and monitor the exact time taken to reach cut off at 60C, also a full set of readings during its run including cylinder top and target temperatures, LLH temperatures etc, can then tell pretty exactly the performance of the cylinder "coil" and might then be able to understand why it should take so long to reach 65C, if required.

Rather than wasting hot water (I am Yorkshire after all), I'll wait until my son has his next shower and take some readings. He has now agreed to always shower before 22:00pm in future!

I don't understand how the system gets the "Cyl temp top" reading. As far as I'm aware, there's only one temperature sensor in the cylinder, wired into the VR 71 and this shows the "Current cyl. temp". As you can see below from the VRC 700 settings, the "Cyl temp top" is shown within the Buffer cylinder menu. The "Cyl temp bottom" has NEVER shown a value. So how does the VRC 700 get the value for "Cyl temp top"?

 

[John.g]

Don't know but in post #77 it was 73c and now showing 68C so must be sensing it somewhere?. a bottom temperature if available would reflect the mains temperature in general and the current cylinder temperature where the sensor is would normally be located maybe 100/150mm above the cylinder coil return as you require the reheat process to begin when a small vol of hot water is drawn off . you will, in any case have a almost full cylinder of hot water available at the target temperature.

 

[milleniumaire]

Don't know but in post #77 it was 73c and now showing 68C so must be sensing it somewhere?. a bottom temperature if available would reflect the mains temperature in general and the current cylinder temperature where the sensor is would normally be located maybe 100/150mm above the cylinder coil return as you require the reheat process to begin when a small vol of hot water is drawn off . you will, in any case have a almost full cylinder of hot water available at the target temperature.

Yes, the top cylinder temperature figure does seem to vary.

There are no other cables from the cylinder to either the wiring centre or the boiler, apart from the temperature sensor that is wired into the VR 71.

Another question for Vaillant technical support I think as it would be useful to understand the origin of this VRC 700 menu option. Possibly also, why is there a top temperature value and not a bottom temp setting.

 

[John.g]

With no cylinder sensor the closest temperature to it is the boiler flow temperature, if so, on change over from HW to CH, it should drop very rapidly.

 

[Ben-gee]

I imagine that the bottom cylinder temperature is available from some cylinders - but not the one you have.

 

[milleniumaire]

Hi John, I understand what you are suggesting, but as things stand I/the engineer have received different advice from different Vaillant support people, so I need to understand why they are making these different suggestions, hopefully once they respond to my email.

What they actually told me in the last email was:

"I would advise to remove the VR40 and wire the single system pump as shown in the example diagram below with a permanent 230V supply to the grey wires and use the oranges from all zone valves wired to the pump live."

View attachment 47032
So, they are essentially wanting to turn the external pump on and off whenever any of the zone valves open or close, which I believe is what the engineer was originally considering doing, but then got confused looking at the schema diagram they had supplied (see attached) and called Vaillant, who told him he needed to use the VR 40, which he then ordered and installed the following day!

It's an interesting thought about using R4 for the external pump, however in the schema diagram it does appear to be associating R4 with the cylinder, so my gut feeling is it is likely to only operate in DHW mode, but as you say it may be worthwhile testing it, but I'll wait until I have more clarity from Vaillant. Maybe they'll suggest yet another way of wiring up the pump

EDIT: Just seen your post from 11:36 last night, so it appears we agree about R4.

Just received the following confirmation from Vaillant regarding the wiring of the external pump:

"With D.27 set to 5 the external pump will only run when the burner is on for DHW or CH as this is for an external solenoid valve so when the burner switches off so does the external pump which does not allow for any pump over run.

The number 5 setting in D.27 external solenoid valve I have only used for a commercial application with an external gas solenoid valve or it has been used for a commercial application when a building management system requires a run and fault indicator. I asked my manager if he new of anyone in or outside technical that would use number 5 for an external pump, which he did not.

I think the best and only option is to disconnect the external pump from the VR40 and use the orange wires from all the zone valves to activate the single pump, this will ensure the pump continues to run all the time each zone valve is open.

I apologise for the conflicting information however the diagram shown below is the standard Vaillant diagram to control a single external system pump the system side of a LLH."

They have included the same diagram as before.

Very frustrating! Not only did I have to purchase a VR 40, but I had to pay the engineer to come back the following day and fit it and now I'll have to pay him to come out, remove it and rewire the pump - in the way he was originally going to wire it until told differently by Vaillant. They really should be accountable when they give bad advice!

One thing that confuses me about the diagram. I assume the SYS.FLOW is the external pump and this clearly shows the live wire from each of the heating zones (and the DHW, which isn't applicable in my case) being used to switch the live on the pump, but where are the neutral and earth wires for the pump connected? I assume my heating engineer would know this, or would he need to call Vaillant again, for yet more bad advice?

 

[John.g]

It should be easy enough to pick up a N&E somewhere, I wonder what logic the boiler uses to determine if any of the zone valves are open if it doesn't get a input back from them?. Why do you say ("and the DHW, which isn't applicable in my case)", don't you need a feed back from the orange wire on that Mot.valve as well.?