Odd pump/stat behavior :-S

[Dazzathedrummer]

Hi,
We had a burst pipe last week, I was decorating and stood on a set of steps and one of the legs went through piece of floorboard that was cut for elec access, the stool leg wend straight down onto a central heating pipe and broke a join! Fortunately I keep a rubber bung next to my header tank so there was minimal loss of water.

We had some trouble finding a plumber at short notice but we noticed an offer from British Gas which basically covers all accidental/emergency repairs plus you get an annual boiler service all for roughly the price of a boiler service. My wife spoke to them and we had a guy out the next day.

He fixed the pipe in no time and serviced the boiler. All seemed fine - it was a hot day so we were happy that it was all firing up properly but didn't leave the heating on.

The next day was quite a bit colder and we switched the heating on - there's only the two of us at home so I tend to leave the immersion heater on for water, leave the CH on constant an use the thermostat to control the heat.

The heating came on and the house got hotter and hotter - I turned the thermostat right down and the house continued to get hotter. It was then that I noticed the thermostat wasn't making any difference to the boiler - with the stat turned right down, the boiler was still firing up. I went upstairs to switch the CH to 'off' on the clock, the red light went out but the boiler continued to fire up and the pump was pumping continuously (even when the boiler was off).

It all worked fine before it was 'serviced'.

Whats going on with my heating?

We've resorted to turning the boiler on and off to control the heat!

 

[stem]

Much will depend upon the accessories fitted to your system, and you don't give us much to go on. But here are a couple of common causes of the symptoms you describe.

If your system is what is known as an 'S-Plan' it is possible that the central heating motorised valve, possibly due to not being used much during the summer has become stiff, opened but then stuck in the open position even though the thermostat and programmer have switched off. When the valve is in this position, a small switch is operated inside it that triggers the boiler and pump. If yours is such a system and you can find the motorised valve, there will be a manual lever on the side of it that if the valve is closed will offer resistance when operated. On the other hand if the valve is still in the open position the lever will be loose and floppy.

On the other hand if you have a frost protection thermostat somewhere (eg. garage / outbuilding etc) and it has been turned up perhaps for testing and not set back to its frost protection setting, that will override the room thermostat and programmer and keep the heating running.

Other than that, you will probably need someone with a good understanding of the wiring and operation of central heating systems armed with a multimeter to test the wiring back from the boiler to determine where the spurious live supply is coming from.

 

[JohnD]

a 3-port valve

looks like https://www.screwfix.com/search?search=port+valve

can you find one?

 

[stem]

With a 3-port valve, the microswitch is fed from the white wire via the programmer and thermostat, so even if the valve were sticking in the heating position it wouldn't energise the boiler and pump when the stat / programmer were off.

With 2-port valves the microswitches are permanently live, so a sticking valve can cause the boiler to stay on.

 

[ianmcd]

sounds like he manually opened a 2 port valve to fill the system but it hasnt went back to auto

 

[Dazzathedrummer]

I’ve got a ‘mid-position actuator’ - a white box that looks like the 3-port valve in the Screwfix link above.

 

[terryplumb]

Contact BG ,if you haven't already ,get them to sort it.