Thermostat Mystery

PC1985

Hi,

Hoping someone can help as i think it is something simple i am missing

We have an old potterton boiler (not combo) which does the hot water and central heating

The CH comes on and is controlled by 1 thermostat in the hallway. Normally when the CH is on, and thermostat goes below the desired temperature, the CH will fire up until temp is reached.

Today however, it isn't working. The boiler fires up when i need it to heat up the water tank, but when i turn the CH on, despite the thermostat showing it is not at desired temperature, the boiler does not fire up (almost like its being told not to fire up / there is no signal telling it to fire up).


As a short term fix, I have currently taken off the 3 way valve switch so when i turn the hot water on i can manually turn the knob so it feeds the radiators instead, but not ideal. And because of the weather (I'm in scotland!) the emergency plumber isn't able to come out until Saturday.

Has anyone had an issue like this before? Or may know what could be causing it?

Le_Kirk

Sounds like the 3-port or diverter valve is not moving, which explains why it works when you move it manually. Normally the thermostat tells the valve to move and when it hits the limit switch, this call the boiler to fire.

PC1985

Thanks for the reply.

i don't think its the valve (me manually turning the valve doesn't turn the boiler on, just diverts water from the hot water tank to the radiators when the boiler is already on)

It feels like its before that, like no signal is going to the boiler from the thermostat to tell it to fire up and change the valve to radiators.

Maybe its a faulty thermostat? Just weird that it does still click between temperature reached and not reached and light goes from red (reached) to not reached (green)

bris

You took the actuator off the valve? Put it back on and use the manual lever and lock it into place, if it now fires up then replace the actuator head.


The thermostat tells the motor in the actuator to turn, this then connects to a switch in the actuator and it's this switch that tells the boiler to fire.

PC1985

Thanks, so I've put it back on valve, and on manual and now boiler switches on when thermostat asks for heat.

What does this mean then, that i need a new actuator?

bris

It's not the thermostat firing the boiler, it's you manually moving the actuator into position for fire the boiler.


The most likely suspect is the actuator motor so you can buy a new head and just replace it.
The fact the thermostat still clicks suggest it's ok but you can't rule out that being the problem. Replacing the stat with a like for like is easy and you can use the existing back plate as it's already wired.


The stat will be far cheaper than the head. There is a way to test the stat with a multi meter but I will leave that to you to google yourself.

jamesperrett

It may be a silly question, but do you have enough water in the radiator system? The water pressure is the first thing I'd check.

PC1985

legend thanks, both seem simple enough to change as i can buy a like for like and its just a few wires.

Ill see what the plumber says tomorrow first (might be covered as part of home emergency cover)

PC1985

Thanks but looks like its a problem with the actuator!