Hi, my name is Mike and I have been in the home improvement and repair field for 20 years. I will be glad to help you today. If the pilot is staying lit then the thermocouple is not the issue. The thermocouple senses that the pilot is lit. Is there any error code?
If you remove the cover and inspect the tubing on the pressure switch there may be a crack or blockage in the tubing. If you shut off the power and gas to the unit and remove the cover and inspect the tubing and be sure it is clear especially in the ports of the pressure switch I am pretty sure that is the issue. If not let me know and we can look into it further. If there is an error code please supply that information before checking out the pressure switch tubing. The code may be an indicator of something totally different. Mike
I don't think you understand just how old this boiler is. There is no digital display to have an error code, as stated at the beginning of my question "I have an old Potterton RF125 boiler..."
Also, as I am not gas safe registered, I would not be eligible to fiddle with this appliance. Insurance would not allow me to.
I understand that the suggested repair is not something that is in your comfort zone. I am unsure why that translates into poor service but I am trying to help by supplying the information that can help solve the issue. An error code can also be blinking lights in a series that help define what is at issue. I hope you understand that I am trying to help the best I can. Mike.
I am more than comfortable to attempt this repair, however, as the boiler is in a commercial premises I would not be allowed to attempt it in line with my insurance company's instructions. I know that this is odd as most people are asking advice to repair a fault themselves, however I am asking so I can be clued up when a plumber arrives to repair and don't get stung for hundreds/thousands of pounds.
Also, the boiler has no display of any kind, no lights, no screen, nothing. It is from circa 1975, all I have to work with is pipes, wires extremely minimal words and numbers, gas control valve and a thermostat.
Well all I can tell you is what it could be. If there has not been regular maintenance and flushing it could be a blockage in the heat exchanger, there may be debris in the burner area, The gas valve could be failing and needing replacing. The repair will likely be a cleaning and possibly heat exchanger replacement or gas valve replacement and possibly a pressure switch or tubing on the switch to replace.