Vaillant Ecoplus 837 combi condensing boiler - DHW problem

13 Nov 2007
Reaction score
United Kingdom
Had Vaillant installed in June 2007 - full system flush on rads etc. Had new bathroom fitted month later with mixer shower & mixer sink tap. All worked perfectly for three months.
In September 2007 the inline cold water feed to the boiler was turned off at mains to refit an in line filter which was leaking. Since that time problems have occured with hot water supply. Central heating okay.
All hot water taps in house can run luke warm without warning. If the taps are runnning luke warm and bathroom shower is turned on (even if it is turned on and off quickly) all taps then run hot. Hot water will then continue without problem. Then problem can return when shower is used again (but not always!). Sometimes problem o*ccurs without using shower. If the taps run luke warm again the problem is always rectified by turning shower on and off.
When the hot water runs hot there is a slight difference in water pressure i.e. water pressure from taps is slightly stronger when running luke warm.

Is it a gremlin - no-one seems to have an answer!!
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Some of these left the factory with faulty dhw ntc's. Could be aquasensor fault.

When running luke warm, press the 'i' button and see what 'S' code is showing.

Boiler is obviously well within its 2 year warranty
Thanks for the quick response - did check when system was runnnig luke warm and came up with code S.14 Burne ignited.
Hi Westcroft try isolating the hot & cold supplies to shower may be shower at fault 'letting by'.
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if the boiler is 5 months old, call vailant to rectify the fault. all you have to do is look up your benchmark sheet to prove it was installed correctly and they will send expert engineer to repair free of charge. why waste your time finding out what the problem is yourself?
shower non return valve letting by cold to hot cooling hot water. measure temp of water coming out from boiler. I bet its hot but is cooler at tap.
Or run shower until hot then run another hot tap whilst feeling hot suuply to shower. I bet it goes cold straight away.
From westcroft. It looks like the shower valve - when runnning hot tap luke warm I can actually hear the water running through the shower unit if I press my ear to the shower. Noise stops when tap water is running hot.

Shower company very good - sending two new elbows f.o.c. with non return valves by post. Hopefully this will cure the problem - will update site when received and fitted.

Thanks to everyone for help.
Had this before,with new boiler,and complete refit,easy way to test is shut off cold into boiler,therefore in theory killing all hot taps.
Opened hot tap and i had a flow of (cold) water,traced fault to one of these walk in steam cabinets with radio and all that carp in.Only problem the bl00dy thing had been built into a corner.Oh what fun!

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