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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> No Hot Water https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1135079327 Message started by Banjo on Dec 20^th, 2005, 11:48am

Title: No Hot Water
Post by Banjo on Dec 20^th, 2005, 11:48am

After 3 years of faultless operation, my Baxi Combi Instant 105E boiler is now struggling to produce domestic hot water. Its OK if I turn the tap on full but even at a flow rate of 6 litres a minute it doesn't heat up. The book says the minimum flow rate for operatioion is 2.5 l/m. There are no flashing fault lights and everything else is OK. Input pressure at the stop tap is 4 bar, central heating seems fine. I rang Baxi and they quoted £259 to fix it (repeat £259). Is there a DIY solution? ???

Title: Re: No Hot Water
Post by CWatters on Dec 20^th, 2005, 11:53am

Quote:

Its OK if I turn the tap on full.

So if you turn the tap on full the water heats up ok?

If you turn it on a little bit it's not OK?

Title: Re: No Hot Water
Post by Banjo on Dec 20^th, 2005, 12:51pm

That's right. As I said, I can turn the tap on a fair way (giving a flow of 6 litres a minute) before the boiler fires up.

Title: Re: No Hot Water
Post by CWatters on Dec 20^th, 2005, 6:46pm

I think (I'm not a qualified plumber) that Combi boilers have a sensor that detects the difference between input and output pressure. I think they use that to detect an open hot tap and fire up. Anyway it sounds like that sensor on the boiler is faulty. Baxi might be expensive but have you tried a local Corgi plumber?

Title: Re: No Hot Water
Post by Banjo on Dec 22^nd, 2005, 12:04pm

The "differential valve - DHW" seems to be the bit that detects that the tap is on and thus triggers the burner, pump etc. If this is faulty then I may have found the solution. I'm still hoping that someone may respond who's seen the same problem before and can verify that a replacement valve fixed their problem.

The local Corgi plumber has had a look at the boiler and is willing to get and fit a new valve but he doesn't sound totally confident that it'll improve matters. Also, he didn't seem convinced that a tap turned "half on" should trigger the boiler to fire up.

Title: Re: No Hot Water
Post by billythekid on Dec 22^nd, 2005, 5:17pm

if it worked before then it should still work. Have you had any other works done to the system at all?

Sounds like the diff valve to me, when was it last serviced?

Scruff will be along in a bit with more info probably(he'll ask you for every detail so have it ready!) lol

btk

Title: Re: No Hot Water
Post by CWatters on Dec 22^nd, 2005, 5:40pm

Did some googling and found this...

http://www.baxi.co.uk/products/literature/Baxi-Combi-80e-105e-Manual.pdf

On page 6 bullet point 7 implies a flow rate of 2.5 l/min should be enough to fire the boiler.

Also this for another model in the range...

http://www.potterton.co.uk/products/literature/performa24iHeInstallation.pdf

....has a fault finding flow chart. On page 43 it suggests the boiler should also switch on when the flow rate is more than 2.5 l/min.

It says that if it doesn't switch on and the flow rate is ok (eg more than 2.5 l/min) you should check...

"Is mains water filter and differential assembly clean?"

If you've got a mains filter on your model give it a check.

If the filter is Ok it suggests you check if the "DHW flow valve diaphragm is damaged.?" I guess that's equivalent to the Differential Valve on yours so it looks this is the right track acording to the book.

If it's not that then I can't think of anything else to try.

Title: Re: No Hot Water
Post by Banjo on Dec 24^th, 2005, 12:58pm

The problem developed out the blue - no other works have been done to the system. I dont think that the servicing has included any diff inspection.

I've loaded down the manual - I may decide to leave well alone until after christmas - just in case I make things worse and can't get hold of a plumber . If hot water fails totally - nothing to lose - so I'll have a go at the filter and then check the diff..

Title: Re: No Hot Water
Post by Banjo on Jan 4^th, 2006, 3:01pm

Bought a diaphram fot the DHW diff this morning - expensive bit of rubber (over £9 with VAT) but £250 cheaper than the baxi call out fee. Instructions in the manual looked straight forward so I did what it said - took out the old diaphram (didn't look damaged, just a bit old) and fitted the new one. I also cleaned a bit of scale from inside the diff assemby. And....

PROBLEM SOLVED!!!!!!!!!

Thanks for your help.

Title: Re: No Hot Water
Post by billythekid on Jan 4^th, 2006, 5:52pm

wtg banjo, and wtg CW for some good advice..

btk

Title: Re: No Hot Water
Post by CWatters on Jan 4^th, 2006, 6:17pm

wrote on Jan 4^th, 2006, 5:52pm:

wtg banjo, and wtg CW for some good advice..
btk

Blush.

Title: Re: No Hot Water
Post by WOLF on Jan 4^th, 2006, 7:38pm

you miss spelt that CW , he said it was a bit of scale etc, so it's FLUSH!!!! LOL ;D

Title: Re: No Hot Water
Post by JerryD on Jan 4^th, 2006, 11:44pm

I reckon CWatters will be "Member of the month" for that!