Central Heating Issue

[Dis86]

So, to start I have already spoken with two plumbers but had conflicting advice.

The issue is that our boiler is constantly running. We have 2 heating loops. Upstairs is cold, apart from the heatsink. Downstairs is stuck on. I've turned both thermostats off. I've reset them. I've disconnected them. I've switched them round. Nothing. I've reset the control panel. Nothing.
The only way I can get the boiler off is to turn it off physically on the boiler or with the isolator.
No errors are showing on the boiler, thermostats or control panel.
The water pump is running constantly, even when the boiler is turned off.

Does anyone have the slightest clue where to go? One plumber has advised the likely cause is one of the control valves for one of the loops being stuck open. The other thinks it's an issue with one of the thermostats.

 

[andy_mk3]

Control valve would be my bet. For dual zone heating, it’s likely to be wired so that the thermostats trigger the valve to open, and once the valve is open it hits a micro switch which then sends power to the boiler.

Valves usually have a manual override lever on them, it’s worth trying that. Amazed a plumber hasn’t tried that, it’s a super common fault.

Edit: so if the valve is stuck open, it will still be closing the switch to call for heat from the boiler whether the thermostat is on or off.

 

[Dis86]

Control valve would be my bet. For dual zone heating, it’s likely to be wired so that the thermostats trigger the valve to open, and once the valve is open it hits a micro switch which then sends power to the boiler.

Valves usually have a manual override lever on them, it’s worth trying that. Amazed a plumber hasn’t tried that, it’s a super common fault.

Edit: so if the valve is stuck open, it will still be closing the switch to call for heat from the boiler whether the thermostat is on or off.

Would that be the strom sszv2222's?

 

[Mysterae_]

I agree with @andy_mk3 , it's highly likely to be a faulty zone valve, stuck in the open position. From a quick google of strom sszv2222 that looks like the one.

 

[andy_mk3]

Would that be the strom sszv2222's?

Yep that’s the one. One end will have a lever you can unhook and manually move. Often moving it manually will unstick it and it’ll carry on working.

 

[Dis86]

Yep that’s the one. One end will have a lever you can unhook and manually move. Often moving it manually will unstick it and it’ll carry on working.

Checked those. On one the lever is as you say, the other, which is for the downstairs loop is loose. There's no resistance.

 

[Mysterae_]

Here's the inside of one of those valves, I had to replace one recently myself.

That brass paddle moves down and activates the micro switch at the bottom and switches on the boiler and pump(s).

What to do next depends on how competent you are with electrics.

 

[Dis86]

Here's the inside of one of those valves, I had to replace one recently myself.

That brass paddle moves down and activates the micro switch at the bottom and switches on the boiler and pump(s).

What to do next depends on how competent you are with electrics.

Did you just replace the actuator rather than the full valve?

 

[Mysterae_]

You can just change the actuator (and it's much easier!) but I replaced the full valve as I'm refurbing the heating system. I doubt you'd need to replace the whole unit unless rubber ball in the valve is stuck. I got one (Honeywell) from Amazon of all places.

Quite simple to remove, remember to switch of the power and make a note of where the wires go.

 

[Mysterae_]

Just had a thought - with the actuator removed make sure you can move the spindle of the valve body (with the pump not running) to make sure it's not stuck.

 

[Chatty72]

I had a similar issue with my boiler and it was a split diaphragm in the diverter valve.