Worcester Heatslave water too hot!

[action]

Although I have read through this topic
http://www.diynot.com/forums/viewtopic.php?p=977851#977851

and has shed some light on things, I still have trouble understanding why, intermittently, I have no control of my hot water temperature from the thermostat switch on the front panel!
Heatslave 20/25 btw around 15 years old.

I was about to change over the divertor valve the other day assuming it had stuck in the central heating side and was passing water to the tank only regulated by the central heating thermostat, and decided to check its operation. The motor seemed to be a bit sticky so changed the motor. After some lube to the workings it appeared to be operating ok. With the heating on or off the valve was operating on demand from hot water both from the opening of a tap and with the thermostat on the front panel. Next day after some showering etc it seems to be back to the norm of overheating the water and me having no control over its temperature at all with the thermostat on the front panal. The central heating had been switched off for a considerable time so no chance of contamination from that side.
Could be a faulty stat but again changed this about 2 years ago to resolve the same problem to no avail.
Where to go next?
Would appreciate any input on this please and thank you in advance.
Alan

 

[action]

Anyone help?

 

[DaveK68]

Hi Action, I have the same issue with my Heatslave 20/25 it seems. Do you ever esolve your issue?

Thanks

Dave

 

[oilhead]

Check operation of diverter valve first, then make sure that the heatstore is full by checking the auto air vent, then check if the dhw thermostat.

 

[DaveK68]

Thanks oilhead.

The diverter valve is brand new, fitted by my heating engineer just under two weeks ago, and the DHW thermostat is new about a month to 6 weeks ago.

I checked the heatstore auto vent and when I pushed the centre down, water came out - no air.

It played up again this morning - getting very hot and both thermostat controls not responding.

Turning the DHW thermostat to the lowest setting - as far anti-clockwise as it will go, does not stop the boiler from firing up and its heating the water. Something it telling it to keep heating the DHW!

 

[Burnerman]

Is the thermostat phial pushed firmly into its socket?
John

 

[dcawkwell]

The heatslave has no blending valve on the hot water
so you have no control via the thermostat on the front panel.
The control on the front of the panel just controls the temperature
in the heatstore. Not the hot water at the tap.

Other oil boilers have a blending valve to deal with this. The heatslave manual also says about fitting a blending valve if you want a consistent temperature at the tap.

It is possible that the thermostat is faulty but this is easily checked
to see if it is keeping a consistent temperature in the heat store.

 

[DaveK68]

John - yep - I specifically checked this by checking the depth of the pocket with long piece of metal and then ckecking how far the DHW phial is going into the pocket. Also, the split pin on the outside of the pocket is holding it in properly.

Somewhat flummoxed, sometimes it works fine and other times it just gets very hot.

 

[DaveK68]

Hi dcawkwell

it's a new DHW thermostat about 6 weeks ago and this hasn't cured the problem - the heatstore intermittently gets very hot.

 

[DaveK68]

Thinking about what causes a demand for the hot water / boiler to fire up - is it possible that it is a intermittently faulty flow valve?

Dave

 

[dcawkwell]

Hi dcawkwell

it's a new DHW thermostat about 6 weeks ago and this hasn't cured the problem - the heatstore intermittently gets very hot.

I think the problem is although I am not sure without looking at
the wiring diagram the burner fires when the tap is running
and will continue to run all the time hot water is being drawn until
the central heating thermostat cuts in. Try turning the central heating thermostat down.
If you have a big burner and are only drawing a fairly slow amount for a shower the burner will supply a lot of heat to the plate heat exchanger and the water will get hot.

Bending valve required. Warmflow, firebird all put them in their combi boilers.

 

[oilhead]

Is the heatstore full????

 

[DaveK68]

Hi oilhead, it appears to be - when I push down the inner part of the auto vent valve on top on the heatstore it certainlt squirts water out, not air.

Dave

 

[DaveK68]

Just tested my flow switch theory, it appears to be that - it is keeping the circulation pump live & the feed to the burner, if I pull the sensor out of the top of the switch, the live feed is disconnected.

New flow switch I think.

 

[dcawkwell]

Just tested my flow switch theory, it appears to be that - it is keeping the circulation pump live & the feed to the burner, if I pull the sensor out of the top of the switch, the live feed is disconnected.

New flow switch I think.

If the flow switch is stuck on when there is no flow then the flow switch if faulty.