temp fluctuation dhw

[ric]

Hi
Have a problem with DHW on a worcester 240.
when running the hot water full flow it is lukewarm, boiler not cycling. When gradually decreasing flow rate water quickly becomes very hot and boiler cuts out then boiler starts to cycle. Seems to be impossible to keep at constant temp.
No sign of flame height altering, even although manual says it is modulating, is this normal for this model?
This model has no user adjustable temperature setting.
Any ideas of cause?
Ric

 

[Billy Bob Bob]

could be all sorts plate heat, thermistor,diverter valve failing best bet get a gsr engineer in

 

[gasmarc]

agree with above could be numerous things but would go for plate to plate if system is mucky and your hot water has been getting progressively worse

 

[ric]

Thanks for reply
but already had one out. He said he thought there were flow rate problems which wernt covered by contract. Flow seem reasonable to me, the boiler does not cycle when the tap is fully open but runs flat out. What I am trying to establish is if this lack of temperatute control is normal behaviour for this boiler,which I doubt, and if so is it the boiler or flow rate.
Any jdea what minimum flow rate should be?
If the boiler is operating correctly should the flame height visibly alter when flow reduced?

 

[stevetheplumber]

sounds like your expecting to much from a 24kw boiler youll be lucky to see 7 litres of useable water in these conditions

 

[ric]

Dont think I was explaining it properly. Wasnt expecting the water to be hot at full flow.
The problem is when I turn the tap down very slowly the temperature should go up. But just cant get it to stay between warm and scalding then the boiler cuts out.
Is this a boiler problem or a lack of supply flow rate?
Need to know the min input flow rate for this boiler before I can get british gas back out.

 

[Billy Bob Bob]

look at the link on here for Worcester instructions but min flow rate would be around 2.5l/min,and reading your posts i dont think this is your issue i would be looking at the diverter valve or plate heat if you have a decent water flow through your hot taps then its defo not the issue component failure get them back out

 

[ric]

Thanks for help, will measure flow rate tomorrow and get them back out

 

[gasmarc]

dont forget the incoming water is very cold which maybe something to do with it

 

[ric]

certainly thats the reason for for it not getting hot at full flow but doesnt explain why the temp wont stabalise. Had a look at it myself this morning flow rate is 14l per minute so its not that. Voltage at modureg is altering as it should be but no sign of flame height altering but not sure whether I should see this or not.
Anyone shed any light?
Will get the british gas back out. Thanks again for the help

 

[binskerb]

Same problem with a Glowworm Betacom. DHW dial has little effect on HW temp. Boiler is not modulating, stuck modulator valve. I suspect new gas valve.