intermittent hot water from vaillant combi vcw sine?

Thanks today it seems that all the hot water taps work for a period of time then run cold. The water pressure seems more than adequate at all the cold taps though a little slower from all the hot taps which I thought was usual.
I am going to get a heating engineer in to service the boiler and hopefully rectify the fault. The boiler has't been serviced for quite a while.
thanks all the info.
Chris

Chris Jones
May 2007

Does sound like a water flow rate problem.When you first open the tap you are on standing pressure. Once the tap is open it's running pressure which will gradually slow down if there are any restrictions like the main stop tap not fully opened.
Sometimes people fit ball-o-fix valves to the pipework when changing baths e.t.c so they can still use the water in the rest of the house. These valves have quite a narrow bore and can cause a restriction.
Can't really tell much more, but if you have checked every thing is fully opened and no restrictions you might want to ask the water supplier wherever you sre to test your supply.
You can test in a simple way by opening the cold tap upstairs, if that is also slowing down on it's own then it would point to a supply problem...

T.H.S
May 2007

Thanks for your reply,
Yes, as you say, the downstairs sinks both seem to work fine still. The upstairs sink and bath do in the main work but the hot tap to the bath has a tendency to shut off after a period of time when your back is turned. If you switch it off for a bit then try again it often starts to work again. However, the mira shower never gets hot..

Chris Jones
April 2007

Does it stll give hot water o.k to the remaining sink in the kitchen which i'm guessing wasn't changed?
If so then there may be a supply problem to the new bath etc.
If it is affecting everything the same then you may not have turned the cold water stop tap back on enough. The older vaillants have a regulator mechanism which limits the flow rate of water and is sensitive to the inlet pressure.
If nothing has changed since before the alterations to your bathroom it may just be coincidental and the water section diaphragm could be faulty.

T.H.S
April 2007