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Brian, Plumber
Category: UK Plumbing
Satisfied Customers: 841
Experience:  16 yrs. experience as plumber, including full bathroom and kitchen installations.
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I have a worcester heatslave 18/25 after the summer layoff I

Customer Question

I have a worcester heatslave 18/25 after the summer layoff I started the boiler and the lock out went I checked fuel flow which is fine water heats up The boiler fires for 5 mins maybe and locks out I can keep pressing the lock out button and will get heat to the radiators but always a lock out maybe something needs cleaning ? or replacing?
Submitted: 10 months ago.
Category: UK Plumbing
Expert:  Brian replied 10 months ago.

Hi if your water is heating then it cannot be a burner lockout.
It must be an overheat lockout.
Turn the temperature right down low on the heating dial to see if that helps
I would think it is most likely a limit thermostat that is faulty.

Customer: replied 10 months ago.
I did as you said there was a lock out after maybe 5 mins the boiler ot I assume furnace part did get hot but no heat in that time in rads
process of elimination?
Thank you Michael
Customer: replied 10 months ago.
I have now tried heating dial down and water dial down and better it went off on its own no lock out and came back on in that 5 mins it put heat into the radiator then it came back on and locked out. in the meantime I looked at and touched the diverter valve
little black plastic thing on top of the case I have started up again it has locked out again I will let it cool down and have another go and time it in about an hour
Expert:  Brian replied 10 months ago.
You may want to make sure the circulation pump is working ok after five minutes the closest rad to the boiler should have some heat in it.
Expert:  Brian replied 10 months ago.
Just read last message. it would appear that circulation pump is ok. So it's probably the limit thermostat. Make sure it's sitting in its pocket correctly. Just to clarify. Do you have hot water with no issues
Customer: replied 10 months ago.
OK 5mins radiators heating up and then lock out water is hot
Expert:  Brian replied 10 months ago.
If I was repairing your boiler I would take a guess at limit stat.
If I needed more confirmation I would take a temperature reading of the thermostat pocket once it had locked out. If it was about 90c that would mean it has failed
Customer: replied 10 months ago.
i checked the thermostat on the front cover which I assume is the limiter all looks good from front and back is there any way to check it.....I assume as heat gets to rads that the pump and boiler and oil supply work ok
Expert:  Brian replied 10 months ago.

Your correct if you have a burner lock out due to oil or other burner issues the lockout
button is on the burner itself.

If the pump was faulty it still should not go into overheat lockout, especially as
you turned the temperature down on the boiler.

When you say you have checked the stat front and back did you make sure it is correctly seated in the phial
pocket on the boiler.

The best way to test them is to measure the temperature of the boiler when the stat cuts out.
as suggested in my previous post. if the pocket has reached near 90c and the dial is on low then the stat has failed

Customer: replied 10 months ago.
this is a funny question what do I use to test the temperature a thermometer?
Expert:  Brian replied 10 months ago.

no not really a funny question. You use a probe thermostat.
if you have a meat thermostat available that will go down to about 70c
that will do the job
fire the boiler with dial on low when it cuts out switch it off pull the phial out of its pocket and put the thermometer in it
see what temp its got

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