LP722 Programmer not respecting Thermostat!

[TedF]

We have an intermittent fault with our central heating system installed by British Gas, which we've had them out twice to try and fix but so far the issue keeps coming back!

Our CH/HW programmer is an Drayton LP722 which is set-up with times for the HW and CH to come on.
There is also Drayton Digistat+ wireless reciever wired into it for the thermostat downstairs.

The issue is, when the programmer hits time for CH, it will turn on and heat the radiators regardless of what the thermostat is at.

To test valves etc I took the thermostat up with me and turned it all the way down and then all the way up. The reciever would flash to show it got the signal and the "on" light would illuminate when the stat was turned up and would turn off when I turned it down.
However, regardless of what the stat said and the reciever showed, I would not hear the motorised valve change.

I then turned off the CH on the programmer and immediately would hear the valves move.

This leads me to believe that:
a) The stat and reciever are fine
b) The motorised valve is fine
c) The programmer is not reacting to the stat changes.

Any advice?

 

[Deleted member 267285]

I would say that the switch live from the Digistat is keeping the valve open. Does it need new batteries? Failing that it’s the motorised valve that’s possibly stuck.

 

[TedF]

I would say that the switch live from the Digistat is keeping the valve open. Does it need new batteries? Failing that it’s the motorised valve that’s possibly stuck.

I went and had another play about and think I've solved it... though it's an odd one...
The pump is a a Grundfos Alpha which has multiple pump settings including an auto mode.. all I did was cycle through each mode and then back to auto and now when I turn the stat down I hear a click and a valve whirr and the pump turns off. Turn the stat up and I hear a click a whirr and the pump spins up...

Very odd, but at least I know what to do in future...

 

[stem]

This leads me to believe that:
a) The stat and reciever are fine
b) The motorised valve is fine
c) The programmer is not reacting to the stat changes.

They are actually connected the other way around to what you have theorised above. When the programmer switches 'on' it provides a live supply to the thermostat for the entire period that the programmer is set to be 'on' for. The thermostat is then responsible for opening and closing the motorised valve as required.

When the programmer turns 'off' at the end of its 'on' period, it removes the live supply to the thermostat, so even if the thermostat operates after that, nothing will happen, because it is not receiving any power.

So, the programmer doesn't react to the roomstat changes, the roomstat reacts to the programmer changes. Hence the above advice from @The Novice.

Regarding your theory with the pump, that is also reversed. The pump will be operated by the motorised valve, so when the motorised valve opens, the click you hear is a small switch inside it that operates the boiler & pump; not the other way around. Altering the pump setting won't have any effect on the motorised valve.

The motorised valve, or room thermostat are the usual causes for the problem you describe. This assumes that the wring is correct of course. However, if it is now working as it should do, and the wiring hasn't been changed then that indicates that it is probably OK.

Some boilers have a pump overrun which keeps the pump running for a few minutes after the motorised valve/s close to dissipate residual heat from the boiler. This sometimes gives rise to confusion as it appears that the pump is running when it shouldn't be. Although that doesn't seem to be the case with your system.

when I turn the stat down I hear a click and a valve whirr and the pump turns off.

 

[Stadan20]

I would slap the programmer and tell it to give the thermostat the respect it so rightly deserves

 

[ianmcd]

They are actually connected the other way around to what you have theorised above. When the programmer switches 'on' it provides a live supply to the thermostat for the entire period that the programmer is set to be 'on' for. The thermostat is then responsible for opening and closing the motorised valve as required.

When the programmer turns 'off' at the end of its 'on' period, it removes the live supply to the thermostat, so even if the thermostat operates after that, nothing will happen, because it is not receiving any power.

So, the programmer doesn't react to the roomstat changes, the roomstat reacts to the programmer changes. Hence the above advice from @The Novice.

Regarding your theory with the pump, that is also reversed. The pump will be operated by the motorised valve, so when the motorised valve opens, the click you hear is a small switch inside it that operates the boiler & pump; not the other way around. Altering the pump setting won't have any effect on the motorised valve.

The motorised valve, or room thermostat are the usual causes for the problem you describe. This assumes that the wring is correct of course. However, if it is now working as it should do, and the wiring hasn't been changed then that indicates that it is probably OK.

Some boilers have a pump overrun which keeps the pump running for a few minutes after the motorised valve/s close to dissipate residual heat from the boiler. This sometimes gives rise to confusion as it appears that the pump is running when it shouldn't be. Although that doesn't seem to be the case with your system.

@stem you are starting to sound like Eric mark or whatever he is called, except you didnt mention mothers house, just kidding mate spot on advice as usual