Central heating control unit and room thermostat clicking - affecting boiler

[Richard M-R]

I have an odd problem with my central heating controls which I hope someone might be able to advise on. Just after Christmas the room stat started clicking as if it was passing the set temperature, but doing it as rapid-double clicks, each pair a few seconds apart, going on for a few minutes at a time then stopping again. It seemed to be only doing it when the stat was calling for heat. After a few days, thinking the stat was probably faulty (over 10 years old) I replaced it, and the problem seemed to be solved.

However yesterday the problem started again. The new stat has an LED to show when it's calling for heat, and this was flicking on briefly even when the stat wasn't calling for heat, but with no click. Today I happened to be in the bathroom when it started doing it, and I found that the control unit is clicking as well, with the "on" LEDs for heating and hot water flicking on and off as well. It seems to do it when either heating or hot water or both are calling for heat, but only when both are switched on at the control panel: if I switch either off at the panel it stops.

So, is the control panel on the blink, or is there some other cause - shorting in the mid-position valve motor switch maybe? At present it's only annoying, but sometimes the boiler tries to switch itself on/off at the same speed which can't be good for it, so I'd like to get it fixed before it stops working completely, especially as there's 4" of snow outside and it's about -7C!

Any suggestions/ advice appreciated; I'm willing to try testing by replacement, as I fitted this control unit myself, and can probably do the mid-position valve as long as I only have to do the motor and not the valve itself. Thanks in anticipation!

 

[Doug99]

Could the lines connected to the thermostat be loose? Check tightness at both thermostat and boiler. A loose connection would cause intermittent operation.