Valiant Combi Hot water problem

30 Apr 2006
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United Kingdom
Hi hoping someone can help !!

My vailliant combi doesnt want to supply me with hot water, it runs scalding hot when i put the tap on then goes lukewarm to cold, The boiler isnt firing..

Ive stopped the problem for the minute by increasing the pressure for the hot water flow with a little white knob found underneath the boiler, i know im going to need it looked at, but wondered if anyone could tell me the problem so i dont get bamboozled by science and end up with a huge bill for work that isnt needed !

Cant you tell im a girl !!

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Nope, couldn't have told you were a girl. Blokes don't have psychic powers in understanding internals of white metal boxes either.

This is a common problem, and usually comes down to a sensor being faulty, or more usually an issue with internal sludge or scale. These can be dealt with, but the solution may not be quick and simple.

A similar problem is addressed here:

Ok i will explain a little better, that poster boiler isnt doing what mine is doing

When i put the hot tap on i was getting about 3 seconds worth of really hot water then lukewarm to cold, and the boiler wasnt firing at all, this happened yesterday for no reason at all. ( not fun when you want a bath ! )

After looking at lots of posts, I increased the flow of water with the little white knob underneath the boiler that controls the amount of water going in ( i think ! ) and the boiler now fires and i get lots of lovely hot water !! ( ive now had bath ! )

If i turn the little knob back down the boiler doesnt fire, is it okay to turn this little knob up a bit ? ( rads could fly off the wall for all i know ! )

Ive only been in this house a few months and the previous owners didnt leave a manual or anything for it !

Im happy to call somebody out to it on tuesday but they could tell me the whole flippin system needs replacing and i wouldnt have a clue, so is it likely to be this valve thing or does it not need looking at now its firing again ?
It may comes as a surprise to you but Vaillant have made more than one model of combi over the years.

I'll make an edusated guess that that you probably have a Turbomax VUW 242 or 282.
Black plastic fascia with turquiose knobs and a number of LEDs?
Could be a VCW (white enamel case with upper and lower doors?).

I suspect that the little white knob is the water flow restrictor, when you run the water through at a higher rate it switches the boiler on.

The very hot you got before comes through becasue the hetaing may have been on previously this 'feature' won't go away until the heating season is finished.

The fact that is used to work probably means one of two things.
1) There has been a reduction in the mains wate pressure (very probably in response to the drought).
2) The diapragm (if it's a VUW ) in the bottom of the diverter valve is begining to fail and will do so completely in due course. This part is awkward to replace but cheap to obtain.

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If it a 242/ then its many years of useful service in it yet - they have a tendance not to wear out. Usuallly a new rubber in the valve on which the little wheel is situated that you have been fiddling with will fix it. Probably around an hours work

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