Vailant turbomax 824e hotwater low temperature

stevesw2 · 12 Dec 2013

My friends Vailant 824e is working fine on the heating side but hot water is low temperature around 35 degrees the temperature rises slightly when you reduce flow at tap.
The flow and return don't get hot when hot water is running so thinking it's not the diverter and the hot water doesn't go hot cold the temperature stays constant. I was thinking maybe the DHW heat exchanger or maybe not any advice much appreciated.

arosindale · 12 Dec 2013

Gas boiler has 2 heat exchangers.
1st is inside the burner which heats the central heating circuit directly.
2nd is the DHW where the hot water in the central heating ring circuit exchanges its heat to this secondary heat exchanger.

Slowing the flow rate will allow the water to remain in the 2nd exchanger allowing to acquire more heat from the the heating circuit, making it hotter.

A diverter valve only diverts the hot water from the primary HE to the DHW HE effectively creating a "mini" heating ring circuit that exchanges its heat via the DHW HE.

Sorry, blabbering on...

100% sure its the DHW heat exchanger (they cram up with limescale/crud etc from the water supply)

stevesw2 · 12 Dec 2013

Thanks for the reply would the hot water go hot and cold if it's the DHW heat exchanger as it's staying a constant temperature at the moment just not very hot I also turned down the cold in and this increased the temperature slightly

arosindale · 12 Dec 2013

Its definitely the dhw exchanger. The temperature will not fluctuate, it will just gradually degrade over time, same will all boilers. Reduced inlet flow is the same as reduced outlet flow, it allows the cold water time to acquire more heat, wheras if its passing through faster, it has less time to acquire sufficient heat.

Whitespirit66 · 12 Dec 2013

stevesw2 said:
would the hot water go hot and cold if it's the DHW heat exchanger as it's staying a constant temperature at the moment

Some boilers do fluctuate when the dhw hex is scaled/clogged. However the Turbomax doesn't seem to. The hw temp just gradually gets cooler over time as the problem gets worse.

It either needs cleaning or replacing. If you're confident, you could follow my instructions in the link.

//www.diynot.com/forums/plumbing/how-to-clean-a-plate-heat-exchanger.356402/#2688253

stevesw2 · 12 Dec 2013

Cheers for the reply I will replace it I am GSR but only really do installs so my breakdown knowledge is not the best so thanks for the advice

Whitespirit66 · 12 Dec 2013

You shouldn't have too many problems, it's reasonably accessible. A crows foot spanner is ideal for one of the unions to the hex - the other 3 are easy. A tap wrench will do if you don't have a c/f wrench.

The cleaning may be a hassle, but after doing it on my father's it performed like a new one.

Agile · 13 Dec 2013

Whilst I expect its a dirty plate, I would still do a thermal survey of the boiler and also measure the resistance of the NTC before dismantling anything.

Tony

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Vailant turbomax 824e hotwater low temperature

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