boiler just keeps on burning

[riffraff]

Hi All,

Sitting on our front room tonight and started to feel very warm.
Checked the room thermostat (analog) and it was off.
Turned it down to zero just to be sure but burner was still kicking in.
So thinking the thermostat might be faulty I went to the utility room and checked the horstmann central control unit...all zones were in an off period.
Just to be sure i set all zones to be completely OFF (it looks like this HORSTMANN_CHANNELPLUS_H37XL one http://www.bhl.co.uk/product/HORSTMANN_CHANNELPLUS_H37XL_PROGRAMMER).
Two minutes later I still hear the boiler outside kick in and start burning oil. The house was like a furnace!

Really confused here, i take it the central control unit is screwed?
Only thing i could do was go outside and turn off all power to the boiler.
I wasn't sure if it was a good idea to just turn all the radiators down instead (presumably the boiler itself has some thermostatic control so it wouldn't just keep burning if there were no radiators taking the heated water?)

Any advice appreciated - if it is the unit can i just replace it?

Thanks!

 

[Agile]

The boiler will control its temperature but it sounds as if the pump was continuing to pump boiler output to the rads.

This would normally happen when a motor valve failed open as its normally wired to act as a relay to power the pump and boiler.

Check your motor valve!

Tony

 

[45yearsagasman]

Look for something like these:- View media item 38425 View media item 44939

 

[riffraff]

Thanks to both of you for your quick replies.
I know nothing about central heating systems.
I guess what confuses me is why when the control unit is set to all OFF the boiler still burns oil and hot water is being pumped to the radiators.
Is it because the control unit doesn't actually control the boiler directly as such but just controls the pumps you are talking about...which if open causes the boiler to burn?
Just trying to get my head around this.

Thanks again for your replies, much appreciated!!!!!!

 

[picasso]

Inside the valve that 45yearsagasman posted up is a small switch where one end is connected to a live supply that is not controlled by the timer and the other end is connected to the boiler, this switch is opened and closed by the opening and closing of the valve,(which is controlled by the timer and stat) when the switch gets stuck in the closed position even when the valve closes the boiler and pump will continue to run supplied by this unswitched live supply.

 

[riffraff]

Ah...right, got it.
That explains it, thanks a million.
Just for interest, this is what the pump looks like, although not sure its the exact model.

Thanks again!