HW only comes on for a few minutes. CH is fine

[Biffabacon]

Hi

I've got an Ideal Icos condenser boiler. When it calls for HW only, it fires up OK, runs for about a minute, then shuts off. I've changed the cylinder thermostat, but that hasn't worked. The CH is working fine.

Any ideas what's going on. It's as if the boiler believes that the cylinder is full of hot water after a minute!

Is there anything obvious I should check before calling a heating engineer.

Cheers

Biffa

 

[petertheplumber12]

You may have an air lock in the top flow pipe to the cylinder, if there is a manual vent on the pipe, open the cap half a turn let the air hiss out, when water comes close it and it should be ok, as long as the motorised valve is opening for hot water. If it is a 3 port valve it will be open by default, so you probably have two 2 port valves.

 

[Biffabacon]

Thanks. Tried that, a little air came out but not much. But problem still persists: boiler calls for hot water, motorised valve opens, boiler fires up, hot water can be felt in pipes both side of valve (2 port). 30 seconds to a minute later, boiler powers down, valve closes.

Something's telling the boiler to stop making HW. But what could it be?



biffa

 

[petertheplumber12]

By pass loop is letting water through and that is more time consuming for me to answer, when boiler fires up before it switches off is the return pipe to the boiler getting hot when it should still be cold?

 

[Biffabacon]

Yes. The return pipe does warm up. It doesn't get as hot as the flow pipe but it does warm up pretty nicely.

What does this mean?

Thanks

Biffa

 

[petertheplumber12]

You must have a bypass loop that tees off the flow pipe between the pump and the valves, and then it goes to the return pipe on the boiler. It should have an automatic bypass valve on it but it probably has a gate valve with a red wheel, try closing it and see if that helps, if it does then the red gate valve needs opening slightly and then later changing to an automatic bypass valve.

 

[Biffabacon]

Thanks. It's got an automatic bypass valve with a dial held by a screw. Can this be turned off in the same way?

 

[Agile]

It can be set correctly!

Tony

 

[Biffabacon]

Even fully closed hot water is coming up the return pipe when HW only is selected so I'm guessing the valve is faulty.

Cheers

Biffa