combi boiler hot temp/flow rate

27 Mar 2005
Reaction score
United Kingdom
This problem has seemed to follow me as I had similar experiences in my last house.
The hot water from the combi boiler is fine when you just turn the tap on a little or you're prepared to shower under a dribble but try to get a faster flow rate and the water runs cold. The temperature of the shower also varies even when nothing else is using water.
Is this the DHW heat exchanger and if so, can I sort it myself?
I'm aware that flow rate is reduced by combi as it needs time to heat water, but this flow rate is set by the boilers resistance right? Not how far I turn my taps on?
Thanks for your time in reading this post,
I look forward to any replies!

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YES!!! Thats the one!!! :p
Seriously though, I posted this whilst at my mums over in Ireland hence the vagueness, I'm flying home tonight and will post an update of all the details as soon as I'm back.
Thanks for the prompt reply though.


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Ok. Here's the info...
I am the proud owner of an Ariston EuroCombi type C boiler. It has the (serial number?) A/23 MFFI - A/27 MFFI.
Hope this helps with any advice you can give me.

I had this exact problem with my Vokera Compact combi - when you had the tap on a dribble the water was nice & hot, but anything more powerful - like a shower, caused huge temp fluctuations. Got installer back who found that a flow regulator was in the cold water inlet bit of the boiler - meaning that there was an insufficient flow rate of cold water coming in to cope with the hot water flowing out so the combi kept on cutting on and off every 10 secs or so resulting in fluctuating water temp. When you put on a fast flowing hot tap does your combi repeatedly cut out? Please bear in mind that I'm not a plumber. :oops:

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