Central heating won't switch off

[Hfb37]

Hello everyone, newby tothe site. Hopefully somebody can help with my central heating issue. The central heating wont switch off using the roomastat or programmer. Unless u turn the boiler off. Hot water side works fine. But when boiler fired up again its ok until ch heating needs to be switched off it stays on again. its a y system with worchester greenstaer ri boiler with honeywell programmer and motorised valve and roomastat and hot waterstat. Just changed the head on the motorised valve and the valve is not seized. All I can tell you is when the ch and hw are switched off there is still 60volts coming out of the orange wire from motorised valve to boiler and pump.

 

[45yearsagasman]

How many zone valves do you have? What boiler is it?

 

[Hfb37]

One zone valve, 3 way. Worcester greenstar RI boiler.

 

[oilhead]

Could be faulty microswitch in Y valve head. You need to check circuitry while boiler is still firing when switched off.

 

[Hfb37]

Even though ive replaced valve head with new item and it still does the same thing. Any idea what voltages I should be getting from each wire in and out of the the motorised valve when hw and ch turned off at programmer. Is the motorised valve still spose to be energised when ch and hw are off.

 

[45yearsagasman]

View media item 30560
This may help with voltage readings.

 

[D_Hailsham]

All I can tell you is when the ch and hw are switched off there is still 60volts coming out of the orange wire from motorised valve to boiler and pump.

This is a quirk of mid-position valves.

However, 60V should not be enough to turn the boiler on, which suggests a problem with the boiler. I believe WB boilers are known to do this; possibly a faulty gas valve.

 

[Hfb37]

So could there be an issue with the pcb board and the boiler isnt been told to shut the gas off. Sorry dont really no how that side of the boiler works. Thanks guys for the information.

 

[Hfb37]

The other thing I need to mention that I tryed is if I disconnect the hw off and hw on wires from the programmer at the wire block end the ch will switch on and off using the programmer or roomastat.

 

[D_Hailsham]

Read How a mid-position valve works.

 

[Agile]

Worcester Ri boiler are known for being able to switch on with the spurious output from a mid position valve.

The solution is to add a resistance to neutral at the call for heat input. Perhaps about 5k but must be adequate wattage.

Worcester tech should be able to advise.

Tony