Central Heating – Over running pump – Advice needed

Morning All,

After a weekend of pretty heavy use our central heating system is showing its age a bit 🙁

Sunday night after the heating “clocked off” the pump continued to run despite the boiler being off. I decided that instead or arseing around Sunday night I would just shut down the system and the mains point.

Yesterday I had a period of chin scratching and then fired up the boiler again. exactly the same happened. Boiler cut out when prompted but pump continued to run 😕

I managed to get the pump to shut off by upping the thermostat on the boiler, starting up the system again for a moment then shutting it off. This then stopped the pump as it should.

Let the heating set as usual but at 10 last night the boiler “clocked off”but the pump continued to run 👿

I reset it using the method above.

This morning the heating came on and this time when the boiler “clocked off” the pump turned off too. 😡

I am guessing that something is up with the boiler stat 😕

Any thoughts?

The system is a std boiler, hot water tank. No room thermostat just the stat on the boiler.

Are you sure this isn’t a design feature.

My boiler has a separate pump wired in parallel, so both are switched on/off at the same time by the timer / thermostat.

When it’s very cold and the boiler has been on for an hour or so it will get to the point where the returning water is hot enough to turn the boiler off but the rooms aren’t yet warm enough to trip the room thermostat, so the boiler stays off and the pump keeps circulating hot water to the rads. Eventually the rads dissipate enough heat and the boiler fires again. This cycle continues till the room thermostat shuts them both off.

Up until now (we have been in our house 18 months) it has never done it before 😕

sticky solenoid on pump maybe?

Do you know if your pump is controlled by the boiler or wired in parallel to it?

If the rads are cold when the pump is over running then I suspect the pump is controlled by the boiler and something is bust.

If the rads are hot then its probably all ok.

What he said ^
You need to dissipate the heat from the boiler itself as well – without an overrun water boils inside the boiler when the pump cuts out.

pumps don’t have solenoids….

The solenoids switch circuits on and off. Pumps just pump water.

I think the pump is boiler controlled 😕

Pump is relatively new and does start stop as it should, well most of the time 😆

I have yet to leave the pump to over run for long enough to see if it is still circulating cold water.

Will test tonight 🙂

I suspect that something is fubarred though 🙁

simons_nicolai-uk – Member

What he said ^
You need to dissipate the heat from the boiler itself as well – without an overrun water boils inside the boiler when the pump cuts out.

Ahhh.

So it could just be the system dissipating excess heat? 😕

TJ’s the man to speak to trained plumber and all

Ahhh.

So it could just be the system dissipating excess heat?

Yup – some ‘low water content’ heat exchangers need the pump to keep running – it is controlled by either a ‘pump overun timer’ or a ‘pump overun thermostat’

the stat will keep it running to a certain temperature., the timer for a set period.

Not necessarily a fault. check the boiler instructions for any mention of pump overun.

If it is a pump overrun it should be a max of 15minutes. Leave it for half an hour and see what happens.

Also Combis operate the heating pump after hot water use to get rid of excess heat.

What boiler? Apollo or suprima by any chance?

I know nowt about it but is it the frost stat doing it’s thing?

Try the hot water thermistor, unplug it and see if the overrun keeps going, for want of a better description ours went a bit earthy and caused the central heating to play up and work only intermittently. The PCB and both central heating thermistors were initially changed to no avail; it was only after the hot water thermistor was changed that the system started behaving itself again.

Strange thing was that it on curve for for resistance and temperature but plugging it back in caused the system to FUBAR.

Boiler is a Baxi.

Baxi what?

Nah pumps always run over to cool the boiler down, same thing will happen after using the hot water. That is why you should always have a radiator in your house that does not have any TRV’s on it, so that there is always one one rad for the boiler to dump heat into. This is straight from the mouth of the best plumber in the world.

toys, such generalizations are hardly ever true.

somw pumps are controlled from the boiler, usually via a temp sensor or timer. allow boiler to heat up, turn it off and see how long pump runs for, it should shut off, if it doesn’t then there is a fault somewhere.

Bear – Member

toys, such generalizations are hardly ever true.

OOops sorry Dad. It’s true I should have been more specific, if it’s a combi then the boiler ALWAYS over runs to dump heat unless the boiler has already cooled in use. If you want to diss my gas safe registered plumber (previously corgi for 15 years) who gave me this info then go for it, but what I say is correct. so blow me. 😆

Calm down dear boy, I’m not dissing anyone.

Exactly you have assumed it is a combi and gas fired, it may be neither, which is where my generalization comment comes in.

Oh and I personally have been Corgi and Gas Safe for about the same length of time, also OFTEC for oil, should you wish to diss my comments!!!!!!

Calm down dear boy, I’m not dissing anyone.

Exactly you have assumed it is a combi and gas fired, it may be neither, which is where my generalization comment comes in.

Oh and I personally have been Corgi and Gas Safe for about the same length of time, also OFTEC for oil, should you wish to diss my comments!!!!!!

S’alright I got your point, indeed I did assume it was a gas fired combi… Naughty boy, I’ll go and thrash myself.

Better! Apology accepted, but don’t be too hard on yourself!

Just for devilment, not all combis have pump over-run 🙂

Paul, careful, can of worms!!!!

yer your right.. Maybe.