CH controls not controlling boiler

[chris2012]

My CH controls don't have any effect on the system. With thermostat set to minimum and programmer control set to off, my boiler starts up every half hour or so. It seems to heat the water up to the temperature determined by the boilers own thermostat and then switch off till it feels it needs to heat the system water again. I've tested this by increasing the boilers own thermostat and the boiler immediately fires up. The water is distributed to radiators and water tank, so the house is too warm and energy is wasted.

I've changed the Honeywell dial room thermostat and the ST6400c to a 9400c programmer on a like for like basis and this has had no effect.

There are a couple of Honeywell motorised valves next to the tank. When moving these valves manually there is no spring effect. Should there be? There was on my last different system with very different looking valves which I had to replace in my last home. Also there is a Honeywell 10 way junction box here. Fuse? I can't see a pump anywhere. Is it within the boiler or doesn't this system need one?

The boiler is an Ideal Icos HE24.

Any suggestions to get the system responding to the controls again appreciated.

 

[petit_pablo]

One or both of those valves are stuck open.

There should be a pump somewhere on the system.

 

[chris2012]

Thanks. Is it likely they'd both fail at the same time or could that point to another problem somewhere? The little levers on both of them move freely, no spring action, no pressure needed to move them manually. They're wired into that Honeywell junction box - would this happen if the fuse in the box had blown?

 

[Armo74]

As stated above the valve(s) are stuck. You need to isolate the power remove the actuators and see if you can manually move the valve.

 

[chris2012]

OK thanks again, I'll give it a go.