Compliments of the season to all...

Was at t'mother-in-law's house yesterday. She complained that she can only get decent hot water when the Central Heating is on. If the heating is not on, she just gets tepid water out of the hot taps, from her Combi.

I checked it out and the symptoms (amazingly) are accurate, and I can see no mis-set controls etc. on the boiler

I have a combi as well & ours works just fine (ie piping hot water on demand, whenever) so I guess there's something amiss... Any thoughts would be welcomed. ...

Be true to yourself. That way happiness lies...

This sounds similar to a problem I had once in a rented house. It turned out that there was a 3-way valve which would allow HW or CH or both, and the HW 'part' was faulty, so that HW was only available when the CH was on.

I'm not that knowledgeable with plumbing and since it was a rental I wasn't too interested in the details, but I recall the plumber saying that these types of distribution valves are quite common and it's not rare for them to develop a fault. I think he just replaced the whole valve unit, and it wasn't that expensive.

Lots of possible causes. Most likely candidates are:-
1 Faulty domestic hot water temperature sensor in the boiler.
2 Faulty three way valve in the boiler.

Or if you want the "left field" option......Does she have a thermostatic shower running off the mains pressure water? If so make sure the temperature setting on the shower valve is turned up. I say this because I had this problem and it turned out that the shower thermostatic mixer valve was faulty and when it was set to cool or cold the valve allowed cold mains water to get into the hot side of the system and hence cools the water at the taps. A new cartridge fixes it but it took me ages to sus it.

Best of luck. John
07 HSE Narvick Black
Land Rover Series One
Triumph Rocket 111 (sadly gone!)

could be a partially blocked heat exchanger, they are surprisingly small and block easily.

Diverter valve little rubber diaphragm inside that goes

+1 for Taz. Diverter valve all the way - had exactly the same happen back in March (the cold part of March!!!).

What make is it? For example Worcester Bosch manuals are readily available online and was easy to diagnose.

As an aside, I also had no hot water or heating from 4pm Christmas day till 11.30 this morning - luckily Boxing day at in-laws and Mrs Natwest at work today so not too bad. This time it was the gas valve.... New boiler due for quote in the next few months I think as it's 15 years old!

Taz is right its the most common fault on combis,I swapped mine three times so I got shut and went back to a Y plan and cylinderso bother scince.

Had a Combi years ago, swore I would never have another, thirty minutes to run a bath, if you tried to run it quicker the water was colder, I expect things have improved since then but I much prefer a tank of hot water.

Natwest, had the same as you last year, no hot water or heating from two days before Christmas till the first week of this year, then for the next ten days only for a few hours, BRITISH GAS

Thanks all... the boiler is only a few months old but she's not been able to get the installer to call her back. (Which to my mind is a bit suspicious, even though it came with the right install docs...)

Is it a plumber job to change the diverter? ...

Be true to yourself. That way happiness lies...

Check with the manufactures website if under warranty then they might have a list of repairers who could do it free ?

Contacted Baxi... They're coming tomorrow. ...

Be true to yourself. That way happiness lies...

ad210358 wrote:

Had a Combi years ago, swore I would never have another, thirty minutes to run a bath, if you tried to run it quicker the water was colder, g:

Worcester Bosch, 5 mins to fill bath, very hot water, shower very powerful too, I would definitely have another combi

npinks wrote:

Check with the manufactures website if under warranty then they might have a list of repairers who could do it free ?

Does sound like diverter valve to me but plumbing can throw so some curved ball faults.

Just out of interest I decided against a combi...have same boiler but unvented cylinder in the airing cupboard giving mains pressure and high flow hot water - best of both worlds I think - no tanks in loft!

I'm considering going to a vented tank with combi and tank linked to electric and solar panels when I get round to doing the extension