Lukewarm 'hot' water - secondary heat exchanger already changed

[Neil Sutherland]

Hi, I'm looking for help with a persistent problem. I have a Vaillant TurboMax Plus 837E combination boiler which appears to be in fine working order. However, it provides only lukewarm water to the taps and shower. To date three engineers have looked at it but failed to resolve the problem. The diverter valve appears to be working normally, closing the supply to the radiators when a tap is turned on. The boiler temperature remains stable at 60 degrees or higher. I have had the secondary heat exchanger replaced and there seemed to be an improvement immediately afterwards; but it proved short-lived. As things stand, we are able to get hot water to the en suite shower but only by opening a hot tap in the main bathroom. The tap then runs cold, but the shower is warm! It works, but is very wasteful of water. You'll understand that I'm reluctant to call yet another engineer without having some idea what is going on, so if you have any ideas for things to check I'll be most grateful. Thank you.

 

[Neil Sutherland]

And I'm wondering now whether I should fit flow restrictors to the shower inlets - but that seems to require measuring the hold and cold pressures which I'm not equipped to do. I always assumed the pressures were similar as the hot water is essentially under mains pressure when a combination boiler is used?

 

[diptin dogshi..]

An isolating valve is not a double check valve? Did you do as suggested and turn off the cold isolator then see if the tap ran hot or did you mistake isolating valves for one way valves and eliminate them on that basis? Confused reading your progress update sorry

 

[Neil Sutherland]

An isolating valve is not a double check valve? Did you do as suggested and turn off the cold isolator then see if the tap ran hot or did you mistake isolating valves for one way valves and eliminate them on that basis? Confused reading your progress update sorry

Sorry if I wasn't clear! There are no isolating valves on the shower supply pipes (hot or cold) so I wasn't able to isolate them. More news at the weekend, I hope!

 

[diptin dogshi..]

Very confusing thread this...
Must be my eyes 😵

 

[Vee]

Sounds like the thermistors need replacing. Had exactly this on that type of boiler.

 

[Neil Sutherland]

Success - at least partially. When I stripped down the Grohe shower valves I found that one was missing the non-return valves in the elbows. I've fitted new valves and, while I was at it, fitted flow restrictors on the cold side. I now have hot water at the taps and even the showers are tolerably warm. I suspect there may yet be more to find, but I'm feeling a lot happier - as is the rest of the family! Thanks to everyone who's chipped in to this thread.