Baxi Solo 3 PF boiler / pump problem

[kdLeeds]

I am having trouble getting the boiler / pump to remain on long enough to deliver hot water to all of the radiators.

The pump switches off when the boiler switches off (I might be wrong, but I thought that the pump remained on for a while after boiler switched off to continue circulating the hot water??)

I have removed the vent plug from the Grundfos pump & spun the shaft (which was free anyway) The pump body is very hot to touch (is that normal?)

I left the vent plug out & switched power on to the system. The pump ran for a second & then stopped. Should it have continued to run?

The boiler does not stay on very long before switching off & then on again after a few minutes. Occasionally the overheat light comes on.

Am I looking at a boiler problem or a pump problem?

Any help would be appreciated

 

[D_Hailsham]

Post deleted - see next post!

 

[D_Hailsham]

The pump switches off when the boiler switches off (I might be wrong, but I thought that the pump remained on for a while after boiler switched off to continue circulating the hot water??)

Yes the pump should continue to run, for about 8 mins.

The pump body is very hot to touch (is that normal?)

The water temp will be about 80°C, which is very hot to the touch.

I left the vent plug out & switched power on to the system. The pump ran for a second & then stopped. Should it have continued to run?

Yes

The boiler does not stay on very long before switching off & then on again after a few minutes. Occasionally the overheat light comes on.

Overheating because the pump is not working

Am I looking at a boiler problem or a pump problem?

Probably a boiler problem.

You could check the pump by disconnecting it from the boiler and plugging it into the mains. If it runs continuously- that's good; if it is intermittent or does not run at all - change the pump.

 

[kdLeeds]

Thanks for taking the time to reply.

I have done as you suggested & put a plug top on the pump and it runs ok (although it did take a couple of seconds to start up, but then ran continuously)

So do you think it is likely to be something on the PCB?

A new PCB was fitted 2 years ago, but I don't suppose that means anything

Thanks again

 

[gas4you]

Re-connect the pump back to the boiler and try again. It should have started immediatley on the plug.

You could also see if you have 240VAC at the pump live terminal on the boiler. If you haven't then it is the pcb.

 

[kdLeeds]

Thanks for your help Dave, but now I'm totally confused.

I have re-connected pump to boiler along with a volt meter. Switched potentiometer to zero (so not calling for heat) There is 240v at pump terminal and pump runs.

Switch pot' up to setting 2 & burner lights, pump is still running.

After a while burners automatically switch off, still 240v at pump terminal, but pump goes off when boiler does??

Retried pump with a plug top & it continues to run, so why doesn't it continue running after boiler shut down, there is still 240v at terminal?

 

[gas4you]

From what you post it certainly sounds a puzzle without being there

Are you saying that when the boiler gets up to temp and the burner stops the pump continues? Or does it stop then?

Or do you mean that when the external call for heat is removed the pump stops instantly? When this happens you should get power to the pump live terminal for a further 6 mins as a pump over run.

Not wishing to insult your intelligence, but you are checking the correct live terminal for the pump?

 

[kdLeeds]

Yes, I am saying that when the boiler gets up to temperature and the burner stops, the pump also stops even though there is still 240v at the pump terminal.

You can insult my intelligence as much as you like if it helps to sort the problem. I am checking the voltage by attaching my volt meter probes to the same terminal block that the pump wires attach to (pump wires still attached)

 

[gas4you]

And when the burner fires up again the pump starts again?

It is definately happening just with the boiler cylcling and not stats up to temp?

Does it happen on HW or CH or both?

Sorry, but I'm confused with this one and clutching at straws

 

[AlanE]

Are you measuring the 240v between Live & Neutral or Live & Earth.

Try connecting a bulbholder to the pump terminals (so that pump and bulb are in parallel and BOTH are connected into the circuit) with a low wattage bulb and post back what happens to the bulb.

 

[twgas]

are you sure they (burner and pump) stop together, or does the pump stop first - then boiler very shortly after (no circulation due to pump stopping) shutting down on stat?

 

[kdLeeds]

Thanks to you all for your help & suggestions.

After a few more tests this morning based on your suggestions, this is what happened.

Connected lamp holder & bulb to pump connections (good idea)
Boiler isolator switched on & boiler thermostat set to zero.
Light bulb is on & pump is running.
Boiler thermostat set to 2 & boiler fires up.
After a few minutes, boiler up to temp' and switches off, pump goes off at exactly the same time, but bulb remains on??
Boiler fires up again & pump runs.
Boiler overheat LED comes on & boiler switches off (pump is off, not sure for how long, so could be why boiler overheated. Lamp remains lit)
After 8 minutes the pump starts to work again eventhough I have done nothing & left boiler in overheat mode (is there a thermal cut out in the pump)
After a further 5 minutes (& pump still running) I reset the boiler & the burner fires up.
I then switched off the room thermostat (so no longer calling for heat) & boiler shuts down, but pump remains running as it should.
After 6 minutes power is cut to the pump and it goes off along with the connected light bulb.

I would be very interested in your comments. My thoughts are that there is some kind of thermal cut off inside the pump.

Thanks for looking
Keith

 

[AlanE]

I would say replace pump as it is possible it is not pumping to full capacity and/or sticking.

Possible sequence of events is pump stops turning, circulation stops and as boiler is VERY quickly up to temp thermostat switches off boiler.

 

[Dirkdiggler]

I may have missed something here but are you sure you have the pump wired into the boiler and not the switch live ?

 

[gas4you]

I agree with above.

It is sounding as though the pump is not wired correctly to the boiler terminals.

Perhaps wires are at the boiler, but the other end of these are not on the pump.