Vokera DHW

kezz · 31 May 2006

Have a vokera compact 28 combi-boiler approx 3 years old working fine until recently. However now when using the thermostatic shower the temperature of the water alternates between hot and luke warm/cold. Have replaced thermistors but alas to no avail. The boiler appears to cut out rather than regulate the heat accordingly. Would welcome any ideas?

Agile · 31 May 2006

I assume that the DHW from the basin taps is OK ?

In that case you should be looking at the shower unit ( and its interaction with the boiler! ).

Usually turning the boiler DHW temperature control down from maximum will solve the problem.

Tony

kezz · 2 Jun 2006

Thanks Agile will do. Yes the DHW from basin taps seems ok.

Forgot to say the problem appears a lot worse when the central heating is on. Might this be a potentially larger issue or is there too much demand on the system?

Agile · 2 Jun 2006

A combi boiler can only supply either hot water or central heating at one time if its operating correctly.

I still am inclined to suspect the shower. What happens if you run a hot tap on half flow when you are using the shower?

There would be a fault in the boiler if it really does give heating and hot water together!

Tony

kezz · 2 Jun 2006

Thanks Tony

we can fill a bath no problem through the taps. Although will try your suggestion tonight. Might it be a strainer issue on the inlet to boiler or on the thermostatic valve as they may be restricting the flow which in turn may cause boiler to cut out

ChrisR · 2 Jun 2006

Two routes to hot-cold-hot showers:

1)
If a boiler doesn't get rid of heat quickly enough it can get too hot to control itself so have to cut the gas until it has cooled. Blockages, sludge, weak pumps, slower tap flow rates etc can make them do that. Sludge covers sensors and slows responses until the temp overshoots.

2)
Thermostatic Mixer Valves produce cooler water eg by restricting the hot flow in. That makes the hot hotter with many combis. So the TMV reduces the hot more, until the boiler cuts off, then it all cools down, and you might feel it. Then it all repeats.

kezz · 5 Jun 2006

Thanks Chris R - apologies for delay in reply as I do not have a computer at home.

Will look into the thermostatic mixer this weekend and also drain boiler down to clean out although living in a soft water area and with the boiler being only 3 years old I would be a bit surprised

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Vokera DHW

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