Central heating turns off after an hour or so

[JimSharp39]

new here and apologies for my first post being a question about my own system.
Vaillant Thermocompact 620e
danfoss fp715 programmer
Danfoss hpa2 motorised control valves
Danfoss mechanical in room thermostat

The hot water works fine. The central heating comes on as programmed and then shuts down after about an hour. I believe the mechanical room thermostat is working properly and is calling for heat. If I go to the garage where the boiler is, and move the control lever on the central heating HPA2 to the manual position, the heating comes on and works normally. Of course I have to go and manually turn it off again at the end of the night otherwise the pump continues all night. I initially thought the HPA2 was faulty so replaced it like for like but it persists. The valve isnt binding or tight. I dont think its the fp715 either as it was replaced a few months ago, although I quite understand that occasionally things are faulty, right out of the box.
The house is about 12 years old and the boiler is original, regularly serviced.
Any thoughts as to the possible fault that is causing the CH to turn off after an hour or so, but still be functional by moving the hpa2 manually?
Am obliged!
Jim

 

[rpm]

Whilst I`m no heating engineer I would turn the room thermostat to maximum and just see what happens then.

 

[SJB060685]

If I’m not mistaken this valve when in manual position is connecting end switch with permanent live and boiler live, this will keep boiler and pump cycling on and off. Are you sure the roomstat isn’t at fault causing valve to shut and boiler and pump turn off? Maybe someone can correct me?

 

[JimSharp39]

Thanks gents. I will check the room thermostat again. I was pretty sure it cycled properly but will check it once the heating goes into programmed mode at 1700hrs.

 

[SJB060685]

Dodgy wire connection in room stat maybe? switch live, neutral? These valves are pretty basic, four wires, a permanent live, neutral, feed and boiler live. Can’t be hard to trace the problem

 

[Murdoch]

when the boiler turns off, what happens if you turn the roomstat up?

 

[JimSharp39]

As I recall, nothing happens when the boiler turns off and I try turning the room thermostat right up. However, with every comment pointing at the roomstat now, I am beginning to disbelieve myself now, so I will try that again this evening if the fault reappears. I have had the cover off the roomstat and given it a blast of air (although to be fair there was no visible buildup of hair or stoor).

 

[JimSharp39]

A quick update. The boiler lit up and provided central heating as planned at 1700, the rads got hot and then it went off around 45 mins later. I went into the garage, manually operated the hpa2 and the heating is back on. I turned down the thermostat, it clicked and the heating went off. I turned it up and it came on...so Im fairly sure the roomstat is ok....

 

[Last Plumber]

A quick update. The boiler lit up and provided central heating as planned at 1700, the rads got hot and then it went off around 45 mins later. I went into the garage, manually operated the hpa2 and the heating is back on. I turned down the thermostat, it clicked and the heating went off. I turned it up and it came on...so Im fairly sure the roomstat is ok..

Is the Boiler going on and off OK for heating the cylinder?

 

[Last Plumber]

You could link out the room stat to rule it out?

 

[JimSharp39]

Thanks for the reply. Yes the hw seems to work, although the timers are the same, so by manually operating the ch, it will run the boiler for both. The hpa2 for the hw seems to be working properly - when in programme, the manual lever is ‘floppy’

 

[JimSharp39]

I will try that tomorrow- you think that even when it clicks on and off properly (when the valve is opened manually) it could still be faulty?

 

[Last Plumber]

If the motorised valve on CH is closing, it will be:-
Switched Live from programmer opening.
Room thermostat opening.
The valve itself (but you changed that so I can't see it).
Or the cables/wires/flex between the above.
It could be a Boiler fault but it doesn't sound like it if you have no issue with DHW. Does the tank warm up in less than 45 min?

 

[Last Plumber]

I would test the live to the valve motor when the CH is calling for heat and the valve has closed. That way you will see if the switched live is still there, then if need be work back.

 

[JimSharp39]

Thanks again for reply. I guess the hpa2 could be faulty straight out of the box, although that doesnt explain why it works for the first hour and then closes again? HW is a very quick heat up. The programmer is fairly recent too so I cant see it being faulty. Could the faulty hpa2 on the hw circuit throw the whole thing off?

 

[Last Plumber]

Thanks again for reply. I guess the hpa2 could be faulty straight out of the box, although that doesnt explain why it works for the first hour and then closes again? HW is a very quick heat up. The programmer is fairly recent too so I cant see it being faulty. Could the faulty hpa2 on the hw circuit throw the whole thing off?

I wouldn't think so.

Wait until it goes off again and check the Voltage on the switched live to the Motor and Neutral. make sure you check the Neutral, don't use a testing screwdriver for this, you need a voltage tester or multimeter.

If you do it that way you will know whether the voltage has gone and that is why the valve has closed or whether there is a fault with he valve itself.

I am presuming you are competent with Electrics. If not then you would be better to get a Heating Engineer or Electrician who is experienced with CH wiring.

 

[JimSharp39]

Thanks again, yes I am a competent diy-er with the correct tools, so will test these in the morning. Have to say this has me baffled!
Thanks again, if nothing else it stops me thinking Im going mad!

 

[Last Plumber]

Thanks again, yes I am a competent diy-er with the correct tools, so will test these in the morning. Have to say this has me baffled!
Thanks again, if nothing else it stops me thinking Im going mad!

No you're not going mad. These things are sent to try us and there are many weird and mind boggling faults that occur on a daily basis.
On the whole anything can be tested and ruled out if you know how.

 

[JimSharp39]

Cheers!!

 

[JimSharp39]

No you're not going mad. These things are sent to try us and there are many weird and mind boggling faults that occur on a daily basis.
On the whole anything can be tested and ruled out if you know how.

Ive tested the hpa2 wiring now. According to my instructions this four wire unit is brown live, blue neutral and the grey and orange are switched.
My test is, heating off and cold:
Brown blue 0v
Blue orange 0v
Blue grey 240v
Grey orange 220v

 

[Burger]

Did you replace the actuator or the whole valve? You might have a blockage somewhere that’s allowing it to get to temperature and turning off. Have you tried the programmer, as in looked to see if it’s off there? Only reason I had a myson one that if I boosted for an hour would sometimes turn off when hot water was satisfied.

 

[JimSharp39]

Did you replace the actuator or the whole valve? You might have a blockage somewhere that’s allowing it to get to temperature and turning off. Have you tried the programmer, as in looked to see if it’s off there? Only reason I had a myson one that if I boosted for an hour would sometimes turn off when hot water was satisfied.

Just the actuator replaced. When I removed the old one, I checked the valve and it rotated very easily and wasnt leaking. The programmer is fairly new, about three months old. It appears to work as expected but Im not sure how it can be tested other than by replacement. To be fair this is the third fp715 ive had in this house in 12 years. Not the most reliable of kit according to the interwebs either.

 

[Last Plumber]

Ive tested the hpa2 wiring now. According to my instructions this four wire unit is brown live, blue neutral and the grey and orange are switched.
My test is, heating off and cold:
Brown blue 0v
Blue orange 0v
Blue grey 240v
Grey orange 220v

If it is calling for heat and you have those readings then there most likely is an issue with the programmer, room stat or wiring.

 

[JimSharp39]

If it is calling for heat and you have those readings then there most likely is an issue with the programmer, room stat or wiring.

Thanks, its pointing to the roomstat as many have suggested! Programmer is newish and the house is less than 15 years old which kinda suggests its not very likely. Appreciate all your thoughts so far mate

 

[Murdoch]

Thanks, its pointing to the roomstat as many have suggested! Programmer is newish and the house is less than 15 years old which kinda suggests its not very likely. Appreciate all your thoughts so far mate

A lot of “new” products are very substandard .......

 

[JimSharp39]

A lot of “new” products are very substandard ...

Agree, this is my third same programmer. To be fair the court of the internet doesn’t rate it, but it fits in the space I have.

 

[Last Plumber]

Thanks, its pointing to the roomstat

I think I said earlier, either test the stat with your meter or link it out. If you link it out an all works well for a day or two you will have your answer.

 

[JimSharp39]

I think I said earlier, either test the stat with your meter or link it out. If you link it out an all works well for a day or two you will have your answer.

Yes, next job! I thought it unlikely at the start but having eliminated almost everything else looks like the guilty party!