VAILLANT COMBI BOILER FAULT Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[chrissy86]

I have a Vaillant combination boiler (VUW 282/1E). It's approx. 10 years old and still working with the exception of the following problem:

First thing in the morning when you switch on the hot water everything works perfectly but when you switch it off and switch it on again, it doesn't work (it stalls). You need to let the boiler stand for 10-15 mins before it restarts again. It needs an interval before it starts as normal. However on the radiator mode it works OK.

What components would be responsible for this intermittent fault? Thanks.

[RusClarke10]

When you say it "Stalls" - does it do anything...Fan run ?.......

If no then this may be due to the micro switch on the diverter valve

If yes then it could be due to scale of the plate heat exchanger.

[chrissy86]

Dear Rus, when it stalls only (unheated) water comes out. The fan does not run, nothing happens. But then you have to switch it off, let it rest for 10-20 mins, switch it on and it starts as per normal. This is a pattern that happens regularly.

I've already changed the DHW (Draw Hot Water) water switch and the condition still remains the same. What do you mean by 'micro switch'? Is this the same thing as the DHW switch?

For this to happen intermittantly with a time-interval rest needed, this indicates to me that it's probably an electrical component where a contact is being made. What do you think are the other variables on the hot water circuit which may give this same fault? (Because on the radiotor circuit everything works perfectly).

Many thanks.

[htg engineer]

You've changed the DHW(Domestic Hot Water) microswitch ?

it may be the diaphragm that is split or stretched - you need to check to see if the diverter is making contact with the microswitch when the water is running - open hot tap, press microswitch manually - if the boiler fires up - change diaphragm.

htg

[chrissy86]

Dear htg engineer,

Thank you for your advice. I have already done what you said; the diaphragm has already been changed, the differential pressure switch has also been changed and so has the DHW switch.

The problem still exists only on the hot water circuit not on the radiator circuit.

Please can you or anyone give me a number of possible answers that could cause this problem, besides above? Thanks.

[alesupper]

Hi Chrissy 86

I have the exact same problem with my Vailant Aquaplus boiler. British Gas have been out to it twice and they have changed the diverter valve but the problem is still there.

Did you ever get to the bottom of this?

Cheers, Alesupper

Dear htg engineer,

Thank you for your advice. I have already done what you said; the diaphragm has already been changed, the differential pressure switch has also been changed and so has the DHW switch.

The problem still exists only on the hot water circuit not on the radiator circuit.

Please can you or anyone give me a number of possible answers that could cause this problem, besides above? Thanks.