Problem with combi boiler Baxi 105e

[Arthur Daley]

Hello everyone, not one to ask for assistance usually but this one has me stumped.

Basically, my central heating doesn't work. It seems to have failed over a couple of days last week. I noticed the radiators downstairs weren't getting very hot yet upstairs seemed ok. Now, from cold, if I turn thermostat higher to enable the heating the pump turns, the boiler fires up and within say 20 seconds the temperature leds increase from lowest of 30 to max of 70 or 80 then the boiler switches the burner off. I'm guessing it thinks it has reached the desired water temperature within the radiator system?

Things I have tried to cure this...

Thinking it was trapped air in system or sludge blockage I have drained each and every radiator around the house individually, draining then partially filling then draining again until the water ran clean.

Automatic air valve on top of pump housing looked caked with hard water crustiness so I have replaced this to aid with the boiler bleeding process.

Finally, I have replaced the pump body thinking that it may have stopped circulating the water, even though I could feel the pump vibrating when it switches on, but this hasn't helped either.

I'm guessing that it is some valve somewhere that is not opening when required. It's worth mentioning that the hot water side of things work perfectly and has had a new diaphragm repair kit done just 2 months ago.

Any pointers would be most welcome before I have to call in the experts to thaw us out

 

[willin]

I'm probably wrong, does it have a pump overrun stat/sensor? it continues to pump the water away from the heat exchanger after the boiler has stopped heating the water to protect the components. If it's faulty the boiler will cut out as you describe (thermal cut out) but still make the hot water warm/hot.

Just a thought as I'm not sure with a combi though

 

[Arthur Daley]

Hello willin, i'm not sure about the sensor, but if I have tried the heating then as you say the pump continues to run for a couple of moments afterwards before it shuts down completely. But the water doesn't seem as if it's circulating to me. Just tried it again and the water is leaving the boiler hot from the outlet pipe for the rads but it only gets to do this for 10 or 15 seconds on burn before the boiler switches off. This should mean that the cold water coming through would col the pipe down again quickly but it doesn't...might be humongous air bubble in system somewhere?

 

[willin]

It usually runs for 30 - 60 seconds, too many things it could be, looking like you need to get someone out mate. Good luck with it.

 

[albob]

Given everything you have done already, you have probably checked this -- is the outside condense drain pipe frozen ??

It happened to me in the last freeze - condensate cant escape from boiler, leading to boiler shut-down

"If the condensate pipe has become frozen, the boiler's sensors will detect that it has become blocked and prevent the boiler from operating. This is a normal safety precaution to prevent damage to the boiler. "

 

[IANB]

Check the condensate pipe is not blocked or frozen And check the condensate trap. Your boiler is displaying classic symptoms of this. My old ideal Isar did the exact same as your describing and it was the condensate trap that was blocked.. I got it fixed but have now replaced it with a new baxi

 

[IANB]

Also seeing you have drained out and re filled your rads you will need to get some inhibitor back in the system. Drain one rad down and put it in that , It normaly comes with a filling nozzle