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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 3629
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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My Potterton (I think 40E) is kettling like a good 'un. I

Customer Question

My Potterton (I think 40E) is kettling like a good 'un. I have flushed, cleaned and added anti corosion Fernox and also the anti kettling fluid but still no goo. However I have also noted that it only seems to fire up for a few minutes, then goes off, only to fire up and within minutes. Could it be the overheat sensor causing a problem?
Submitted: 1 year ago.
Category: UK Plumbing
Expert:  Brian replied 1 year ago.

I would think its overheating i would check your circulation pump before looking at boiler faults if its definitely circulating then start looking at thermostats or thermistors.

Customer: replied 1 year ago.
fyiI recently changed the hot water tank thermostatthanks
Customer: replied 1 year ago.
I can hear the pump running and it does change speed when I flick the switch on it. Could it still be the pump or which of the thermostats etc do you think I should change...there appear to be several:
.Control thermostat 404504
.Pump over run thermostat 404507
.Overheat thermostat 404495
Thank you
Expert:  Brian replied 1 year ago.

Hi Rubin I am going to opt out for you as I think there are engineers on site that know this boiler better than me.

Expert:  Andrew Smith replied 1 year ago.

It sounds like a water circulation problem.

The water is flowing through the boiler too slow, either a restriction in the heat exchanger (scaled up, partially blocked) or the circulation pump is running to slow.

The kettling is caused by the water being heated too fast and boiling in the heat exchanger.

The boiler silencing solution could have made things worse, this works by coating the inside of the heat exchanger to slow down heat transfer but can cause problems as it can block small waterways too.

Customer: replied 1 year ago.
OK. Thank you. What would you recommend. Replace the pump or maybe deadfalls the system? Thanks again
Expert:  Andrew Smith replied 1 year ago.

I would replace the pump and see how you go, it is cheaper than replacing the heat exchanger.

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