Vailant VCW242E - DHW - Only really hot when cold running

[cherrymetal]

Hi,
I've been experiencing a lack of really hot water lately. Its not too bad, but apparently not hot enough for a bath for the Mrs (she seems to like 3rd degree burns!).

I've found that running the cold tap in the sink while filling the bath with hot makes the hot tap in the bath significantly hotter (to her indoors satisfaction). The boiler then cycles on and off while filling, which I believe is so that the water doesn't get too hot.

The temperature for the DHW is at max on the boiler. I had been told before that it can be a symptom of the CH circuit having low pressure, so I've topped that up with the filling loop up to close to 2bar. It does seem to lose pressure reasonably regularly, dropping to around 1bar, never to the point where the boiler won't fire up though. I've not found any leaks anywhere. There is noticeable scale around the heat exchanger, but I can't see any leaks or moisture anywhere, just dry scale build up.

Any suggestions?

 

[JohnD]

this is typical of a combi boiler. It is nothing to do with boiler pressure. It will get worse during the winter as the incoming water will be colder.

Turn the hot tap down a bit to reduce the flow.

A combi can only warm x amount of water by y degrees, in a minute.

If you make x smaller, y gets bigger. And vice-versa.

You might have to fit a reducing valve on the hot pipe to the bathtap if she refuses to turn the tap down. This is typical of wives.

You can also remove the problem by getting a hot-water cylinder.

In your case, it looks like, nominally, "x" is 10 litres when "y" is 35C

 

[cherrymetal]

Thanks for that. Is it something that gets worse? The wife reckons "it was ok last winter" ha ha! Is there anything I can do other than winding down the hot water? I've not messed with it before (water flow), the only thing I have had to do over the years is turn up the temp for the DHW (now at max), I know others with combi's can't get there's anywhere near max, because it then scalds. Mine doesn't! Is it just because its old? (Came with the house, and I've been here 17 years)

 

[picasso]

I reckon the plate heat exchanger is blocked.

 

[cherrymetal]

Can it be cleaned/unblocked or am I best off replacing it? Guess this is what I need http://www.ebay.co.uk/itm/VAILLANT-...519087&hash=item3adbd545d7:g:CkwAAOSw4CFYuXtW seems to be a bit of a price variation, and some come with 3 pipes, some with 4 and some with none. I think I read somewhere this is a retrofit, and is different from the original presumably hence the kit including pipes