Worcester heat Slave 20/25 Oil Combi Hot water problem

[burningoil]

hello, We have a Worcester Heatslave 20/25 Oil Combi (c. 15 years old). It works OK on central heating, the radiators get hot quite quickly and stay hot. Hot water is the problem. When you are in the shower it starts off hot but throughout the 10 mins (that the hot water lasts) you have to keep turning the temp up slightly until you pick your moment to jump out before it starts to go cold. For a hot bath you get some hot water but not really enough to fill a bath. Any ideas? Many Thanks

 

[Burnerman]

On my 12/14 the symptoms were similar - loads of C/H but no hot water.
The motor on top of the diverter valve had packed in.
John

 

[oilhead]

Diverter valve jammed open; change synchron motor.

 

[burningoil]

I am getting good hot water but it only last for 10 mins. I did originally think driverter valve, but would that being faulty allow the temp to slowly decrease over 10 mins?
The expansion vessel was changed at the last oftec service some 11 months ago..
i thought you got unlimted h/w with a combi??
PS I have tried it with h/w only selected and c/h off but it behaves the same - very hot water and then the temp slowly drops off over 10 mins

Thanks

 

[Burnerman]

I'm sure the diverter valve is letting water by to some extent.....you should get good H/W supplies otherwise. The 10 minute supply is due to the heatslave tank, I guess.
John

 

[oilhead]

Switch to hot water only and let the CH cool down. Run your hot water, and feel the CH flow pipe. If it gets hot, then diverter valve is passing.

 

[snb]

i would try what oilhead has stated first.

if the central heating pipes are cold then i would go for descaling the plate exchanger.

But it would be best if you can put some differential temp probes on to see what is actually happening.

It could just be that you are exhausting the thermal store. If that is the case then all you can do is turn the hot water to max.

The only other thing is the engineer may have reduced the burner output.

These are normally set at mid output so the option to increase power by 10% is always there!!