Strange behaviour - Boiler won't turn off unless I use main elec switch

[Davidtdw]

Hey folks, I'd appreciate some pointers on this as it's super confusing.

We have a Gloworm Ultimate Boiler - quite old from previous owners & in 100yr old house listed.

There is a Horstmann ChannelPlusXL below and a Power switch for the mains supply.

A few months ago we discovered that even when the Settings on the Horstmann were for Timer, and the time was for just one hour in the morning set to go on, the thing would be on all day. The boiler light was on and the radiators constantly supplied with heat.

I experimented with using different settings on the Horstmann, including turning it to the 'Always Off' setting, but still, the boiler kept cooking.

Eventually I gave up and turned the Mains switch off, which was the only way to get the boiler to stop running, after which we've just lived without hot water or heating during the summer, not a big deal for us. Now it's getting cold again I'm keen to get this sorted but not sure where to start.

Have you come across this problem before or have any suggestions for what we should do or what kind of help to seek?

Many Thanks!

 

[ianmcd]

you probably have a faulty zone valve seized in the open position should be the CH one if the rads are heating

 

[Harry Bloomfield]

Have you come across this problem before or have any suggestions for what we should do or what kind of help to seek?

It could be the Horstman's relays contacts which have welded up, or the valve actuator which has jammed. Does the Horstman click when you switch the power on and off.

What happens if your turn the room thermostat down to minimum?

Assuming you use the boiler for water heating, when is the Horstman set to come on for heating water?

 

[Davidtdw]

There's a fairly loud click when I turn the power off, nothing continual though.

If I turn the radiators all off, the boiler light goes out, though there's still some whirring upstairs in the hot water tank.

As for heating water, there isn't a setting for that on the Horstmann, I just assumed it did both.

 

[ianmcd]

which channel plus there are quite a few