Baxi 80e - thermistor issue?

13 Jan 2009
Reaction score
United Kingdom
Recently had some work done on my boiler (some o-rings replaced after a couple of small drips). The engineer noticed the rads weren't heating very well after this work and said some sludge may have dislodged and to try to keep running the heating with TRVs open to try and push it through.

Additionally, he said the thermistor was likely shot (said it's been firing between off and full power). Well, that was last week and the rads still aren't heating properly. I also just replaced the thermistor and it looks like the problem remains - it heats to 80c quickly, shuts off, then drops 20c every 15 seconds until it's down to 30c, then the flame comes back on again.

I'll probably look at running some inhibitor through it next, but I should note I've never had any problems with the rads not heating in recent years, despite having periodical work done and drained the system a number of times. Just wondering if it could be anything else?
Sponsored Links
Perhaps the return filter is the front section of the return isolating valve.
Thanks guru, how could that be unblocked?

I also noticed it's 'kettling' again - it had been doing that a few months ago, but topping up pressure seemed to resolve it - but it's back, even at 1.5bar The rad in the hall (no TRV) is quite hot and large one in sitting room is not bad, but the rest are rubbish!
Sponsored Links
Turn off isolation valves far left and far right. Drain boiler.
Remove chrome cap facing you on right hand isolation valve and remove wire mesh strainer. Clean and replace. Re pressurise boiler, vent and voila.
Ok, did as instructed and checked filter but it looked spotless (soft water area). Replaced and refilled boiler but forgot to vent - boiler had a lot of dripping water type noises internally and cut off.

Bled the rads and realised there was a hell of a lot of air in the system (enough to bring pressure back down near to zero after bleeding). But boiler's refusing to power back up (first 2 LED's flashing which, looking at the manual, may be safety thermostat?).
Let it cool, or knock gas off at meter and let it run round cold to get the air out (u will need to keep resetting the boiler as it will lockout without gas)
That's a flame failure and overheat which is an odd combination.

Shut the gas off. Reset the boiler and run the heating, when the pumps quiet run the hot water for a short time. Keep repeating until the pump runs quiet. You'll have to reset each time it locks out from no gas. Now open the gas and try it.

Are you sure the pumps ok?
Thanks, figured to try letting it cool but 15 mins didn't do it (will try again in morning) before trying the gas off route.

Think the pump is solid, engineer said it wasn't running too hot anyway.
A lot of those problems do sound like a blocked/seized pump but unless the pump flow switch was jammed or wired backwards that would not usually happen.

Sounds to me like you need a competent engineer!

Tried it again this morning, within a few seconds the first 2 LEDs were flashing again but I don't even think the flame was on at any point. Then went through the procedure of turning gas off etc but no change.

Will get engineer back out & give him another run at it, he had been recommended.
Check the plug on the overheat stat, they are easily pulled off enough to disconnect the wires even with the rubber boot still, apparently, looking to be untouched.
Thanks, wasn't that though TW.

Had engineer back out. Said return valve was dodgy (though didn't seem to have any issues before he replaced o-rings). Replaced return valve and the other valve next to it (as it had been dripping). Ran some inhibitor through it too - £160. Sound reasonable?

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links