Heating valve not opening when calling for heat

[mazdaq]

Strange things happening with my heating system lately. It’s got 4 separate motorised valves – underfloor heating in new extension, upstairs rads, downstairs rads, hot water cylinder. I assume there is one underlying issue causing these but not sure what the likely cause is and what to check first:

-The other day, woke up around 3am and found the upstairs rads were on even though they're programmed to go off at 9.30pm - room temperature was 24 degrees, and the thermostat is set at 19. The boiler was on and the programmer screen showed that somebody had pressed the arrow button telling the heating to stay on until the end of the next programmed cycle, which would have been around 8.30am. I was the only one in the house at the time and I didn’t press it – although I have noticed mouse droppings in the boiler cupboard so I guess a creature could have crawled across it and pressed it. Regardless, the boiler should have shut down and valve closed once it reached 19, not carried on indefinitely. Turned the whole system off at the mains and restarted it, and it seemed to have worked ok since then, until today that is.

- Got up this morning – the upstairs heating was on, as expected, as the upstairs temp was only 18, but no downstairs heating, despite the thermostat calling for it – room temperature 17. The valve for the downstairs heating was closed – I manually opened it and the rads downstairs started heating up. But once the upstairs heating goes off as it’s met the room temperature, the boiler shuts down and no further heat flows to the downstairs rads.

Any ideas? Wondering whether a faulty programmer is the most likely cause? Or should I start with changing the motorised valve head? Thanks

 

[terryplumb]

You would need to check voltages at the wiring centre to establish why the downstairs heating isn't coming on when it should do. Could be programmer,stat,or zone valve issue.
Likewise when upstairs heating comes on when it's not supposed to ,establish where the voltage is coming from.

 

[ericmark]

In the main, when odd things happen in my house, the culprit is the Google Nest Mini miss hearing what I have said. The idea was not to have voice control for heating, but somehow it has connected to the heating. In some ways good, hey google set living room to 22ºC is easier than accessing three different devices, but I would have preferred not to have smart control.

However, to overheat there has to be at least two faults, the boiler needs to run, and the TRV heads need to open, so the only real problem is when heating does not come on.

I had to wire up my own central heating, and I did a circuit diagram so when I had a problem, I could get it out and remind myself how it was wired. The diagram is not quite correct, but there are two ways to fault find, one take a stab at likely faults, and if that does not work, then follow the circuit in a methodical manner.

Stage one is likely work out how wired, as soon as someone says "under floor heating" I think oh no, that's a job for a heating and ventilation engineer, no longer is it a simple C, S, W or Y plan.