Baxi Boiler - Water gets hot then cold then hot.

MisterFish · 10 Dec 2014

I had a problem with my boiler (Baxi Duo-Tec Combi 40 HE A). It was overheating and then when cool loosing pressure and stopping. I called the guy that installed it and he diagnosed replacing the pressure vessel. This he did, (but at a huge cost – I checked the cost of the part and worked out he charged me a little over £170 per hour to fit). However the fix sorted the problem.

The thing is that since he left the hot water runs alternately hot and cold. A bath full will be just warm.

Can anyone hazard a guess what is causing this and is this something that I can fix myself rather than spend the kids Christmas presents on getting him in again?

Thanks.

ALCPlumbing · 10 Dec 2014

It's difficult without looking at the boiler but sounds like it could be a partially blocked plate heat exchanger. This type of blockage will cause the boiler to get up to temperature too quickly which will cut out the burner until it cools and will then fire up again. This causes the water to come out at inconsistent temperatures, hot, lukewarm, hot, lukewarm, etc, etc.
It's not a boiler I'm familiar with but there's plenty of guys on here that do and might think it's something else.

gigz · 10 Dec 2014

Yeah, agree with above or DHW thermistor. How long has the boiler been fitted ? Was it flushed ?

MisterFish · 10 Dec 2014

gigz said:
Yeah, agree with above or DHW thermistor. How long has the boiler been fitted ? Was it flushed ?

The boiler is about six years old. It was fitted when we bought the house and enlarged the existing CH system. I am not sure what flushing entails or whether it was done at the time we fitted the boiler.

MisterFish · 10 Dec 2014

Just checked the paperwork from when we had the boiler fitted. Yes the system was flushed.

St0rmer66 · 10 Dec 2014

A fixed price repair would have been far cheaper for future reference! Either from Baxi themselves or another company. Extremely unlikely that a 6yr old expansion vessel would need replacing. Simply pumping it up usually sorts it for several years at a time.

MisterFish · 11 Dec 2014

Can anyone point me at any guidance as to how to flush my system?

hanns21 · 11 Dec 2014

Read the instructions in the manual on how to replace dhw plate heat exchanger. Once you have the the plate removed put in a bucket with boiler water and some citric acid power from your local chemist. Leave i half hour then run it under cold water. Re install and you should be fixed.

St0rmer66 · 11 Dec 2014

hanns21 said:
Read the instructions in the manual on how to replace dhw plate heat exchanger. Once you have the the plate removed put in a bucket with boiler water and some citric acid power from your local chemist. Leave i half hour then run it under cold water. Re install and you should be fixed.

Brilliant advice, I'm sure nothing can go wrong there with a DIY'er taking major components out of his boiler!

hanns21 · 11 Dec 2014

Draining a boiler and taking two screws out is hardly major! As for getting charged £170 per hour maybe thats your problem! This site is for advice. If he feels comfortable doing it. Its not rocket science

MisterFish · 12 Dec 2014

hanns21 said:
Read the instructions in the manual on how to replace dhw plate heat exchanger. Once you have the the plate removed put in a bucket with boiler water and some citric acid power from your local chemist. Leave i half hour then run it under cold water. Re install and you should be fixed.

Thanks for taking the time mate.

I checked in the manual. First instruction "Remove gas valve as described in section ..."

Square one!

MisterFish · 12 Dec 2014

hanns21 said:
8.20am in the morning!you really r a sad case. Grow up

He says at 8.36!

45yearsagasman · 12 Dec 2014

Now Now ladies, tis Christmas, be of good cheer. Peace and goodwill to all!

hanns21 · 12 Dec 2014

Sorry i apologise. I didnt realise you were the person looking advice. I thougth it was someone having a go. You should be able to remove the plate without touching the gas valve. Have a look. I cant remember ever having to remove a gas valve to remove a plate. Tho cant remember ever cleaning a duo tec. Its usually just two alan key nuts .

MisterFish · 12 Dec 2014

hanns21 said:
Sorry i apologise. I didnt realise you were the person looking advice. I thougth it was someone having a go.

No problem. Honest mistake.

hanns21 said:
You should be able to remove the plate without touching the gas valve. Have a look. I cant remember ever having to remove a gas valve to remove a plate. Tho cant remember ever cleaning a duo tec. Its usually just two alan key nuts .

Thanks for this I'll take a look. Unfortunetely the in laws are up for the weekend and her dad is mustard keen but much better at DIY in his head than in reality. I'll get to it on monday and let you know what I can find.

Thanks again.

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Baxi Boiler - Water gets hot then cold then hot.

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