Baxi Combi Instant 105e - hot water getting colder

3 Mar 2011
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United Kingdom
Over the last few months the hot water produced by my Baxi Combi Instant 105e went from really hot to warm-ish. I can now get really hot water only when the flow demand is low. When I open up fully a hot water tap the water is warm-ish. The Central heating water is fine though: radiators heat up fine.

Any idea anyone?


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If it were gas settings than that would need a registered engineer to check it.

Much more likely to be a blocked secondary heat exchanger. But it could be other things like temperatrure control or pump etc.

The only way to confirm the heat exchanger is a thermal survey of the boiler.

does the boiler stay on during hot water demand?or cut in and out?if it stays on then the diverter valve could be passing, if it cuts in and out then its prob a blocked plate heat exchanger
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Hi Tony

Thanks for your answer.

Could you explain how you carry out a thermal survey of the boiler?


Hi Paul

Thanks for your answer.
The boiler switches on and off when hot water is on demand.
It is worth trying to unblock the plate heat exchanger or should I change it?(my boiler is 8 years old and where I live the water is very hard)
If I try to unblock it, what is the best way to do it?


they can be cleaned but not always successful, best to get a new one. also get some quotes to have a magnetic filter fitted to the system.
Thanks Paul.

OK, I will buy a new one then.
I just looked at it and it is going to be a hell of a job to remove it from the boiler:It is as packed as inside a digital camera in there. I wish they had put some kind of step by step illustration in the maintenance manual...

Anyway, thanks again.

To be honest it isnt that bad to do, but then again i have changed many! cant remember my first so maybe thats a good sign! get yourself a dhw sensor also, for the sake of a few pounds its worth fitting whilst u have boiler drained!

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