Valliant VCW SINE 18 W - DHW problem

[nerrad]

Hi, can anyone help me with some advice please?

Had a problem with my DHW last winter. The water temperature was low, baths just not getting hot enough. Cleaned out the heat exchanger and was still low. It is hot enough for showers, but certainly not hot enough for her in doors to take the usual tropical bath!

It has been working fine all summer with the ambient temperature of the cold water not that cold.

Now we have just started to use the heating again, the DHW is again not that hot.

Ran some tests today, from a cold start.

ran the hot water and it heated up ok, but not piping hot. there was no heat being dumped into the heating system at all.

ran the heating system and that works fine, very hot rads all round.

ran the hot water while heating system on and it doesn't seem to get as hot as it should be.

One question I have, the output from the heat exchanger goes back to the cold water inlet, via some device with a pressure vessel on it. Is this just a pressure control device to limit the flow of hot water? is there anyway that cold water could be mixing in with the hot water in this device?

Should I try to clean the exchanger again?

I know the boiler is very old now and probably needs replacing, but could do without spending £1000 to replace with a Valliant 831.

thanks in advance for any help/suggestings

Darren

 

[kevplumb]

One question I have, the output from the heat exchanger goes back to the cold water inlet, via some device with a pressure vessel on it. Is this just a pressure control device to limit the flow of hot water? is there anyway that cold water could be mixing in with the hot water in this device?

methinks you mean the dhw expansion vessel

View media item 14780


which heat ex are/have you cleaned

and how

 

[DP]

AND................how much water is flowing out the hot tap? collect for 15 seconds, measure water quantity and post result.

Look at the burner flame. Does it reduce in size when hot tap is run?

 

[nerrad]

Thanks for the quick replies, wasn't expecting that!

The dhw expansion vessel is attached to the device I am speaking of yes. The heat exchanger was cleaned last winter with a chemical cleaner, can't remember which, a very dark copper soltuion came out of it after leaving in for about 3 hours. Can't remember if I cleaned the inside cold water flow pipe or inside the vessel itself now.

Just checked and the hot water flow is about 9l a minute measure from the local tap

thanks Darren

 

[Gasguru]

9 litres/min will just about get the water to bath temperature. Open the tap anymore and it won't be hot enough.

You could open the tap fully and gas rate it (see the FAQ's) just to confirm the boiler is operating at its maximum output.

 

[nerrad]

Thanks Guys, now sorted.

The flow rate was too high.

Back tracking to when the problem started.
I had shut the mains water to our house two weeks back to fix an outside pipe. When I put the mains water back on again I must have opened the valve more than it was before, thus increasing the flow to the house and boiler. The flow control on the boiler itself was not set correctly, hence letting too much water through.

Have adjusted to a flow of around 6.5L per minute and all is well.

Thanks again for the input

regard Darren

 

[DP]

flow should be 9.5l per minute.