Boiler switched off but still coming on!

[davecooper]

The other night, our central heating came on at around 2am, it was timed to come on at 6:30am. After some investigation, we realised that it was not being controlled by the boiler timer and was effectively on all the time after this, even though it was switched to "Timed"

We have Worcester Bosch boiler cover so an Engineer called and replaced the timer and the diverter valve.

Now that the weather has sorted itself out, once he had gone, we switched the CH side of the boiler to "Off" and turned the thermostat fully down. Despite this, the boiler came on during the day and we got back to a red hot house with the radiators all hot.

We are obviously going to get WB back again but has anyone any idea what could be causing this. Boiler is WB Greenstar.

 

[stem]

The 'diverter valve' which is operated by the programmer and room thermostat, normally controls the boiler when the central heating is required, so would logically be the first place to look.

Another area, to consider if the system has a frost thermostat fitted, is that it has either been incorrectly set, or is faulty. A frost thermostat is designed to override all of the other controls and turn the heating on when the temperature drops and freezing of pipes may occur. Sometimes they are a separate item wired outside of the boiler, sometimes they are integral and part of it.

Incorrect wiring could cause this, but if it originally worked OK and the fault suddenly appeared, you can rule that out.

It shouldn't be too difficult for someone with a knowledge of the intricacies of central heating system wiring and equipped with a multimeter to trace where the fault is. Assuming that it is present when they were there.

 

[HootingOwl]

Which model of greenstar is it? Have seen this on the CDi GS combi.