Potterton Promax Combi HE Low And High Pressure, Poor Hot Water

I was asked to service a Potterton Promax Combi HE as it had not been serviced since it had been installed. It was not that old but should have been serviced annually. When I arrived the customer had a list of issues with the boiler which also required investigation.

• The boiler keeps losing pressure
• The water pressure in the system keeps going into the red
• The hot water keeps going hot and cold
• One or two of the radiators were getting hot even though the heating was off

I looked over the boiler and asked if they had noticed any water leaks, which they hadn't. I looked at where the Pressure Relief Valve is terminated outside and could see that there was signs of it having let water out of the system. Having been leaking for while the PRV would require replacing as it was fouled with scale and debris from the system.

I topped up the water pressure to 1 1/2 bar and turned on the central heating system. It was not long before the water pressure in the system had risen and was close to the red. I turned off the heating and drained the pressure out of the heating system and checked the pressure in the pressure vessel. The pressure was low and with the drain point still open I increased the pressure in the vessel to the recommended amount through the schrader valve.

After setting the boiler back up I ran the hot tap and after running off the cold water in the leg of pipework it began to come through reasonably hot, and then cold, and then hot again and kept cycling like this without getting up to a satisfactory temperature. Watching the boiler I could see that it was rapidly getting up to temperature before cutting out, and was not transferring this heat to the hot water. When the boiler got up to it's maximum temperature it would send hot water out to the radiators explaining why a couple of the radiators had been hot at times through the summer. I removed the hot water plate heat exchanger and could see that it was quite badly blocked with debris and sludge from the system.

I replaced the PRV, plate heat exchanger and fitted a Adey Magnaclean filter to the system to protect the boiler from getting blocked again in the future. The system was only three years old and had been completely repiped with new radiators and treated with chemicals and yet surprisingly was in quite a bad state. I believe that some of the old pipework must have been re-used under the floor which was already fouled with scale and debris and not cleaned sufficiently when the new system was installed. Hopefully the Magnaclean will pick up the worst of the debris and keep it working as it should be.

Disclaimer: The works described in this blog are a record of work undertaken and should not be taken as guaranteed to solve your problem. Work should only be carried out by persons qualified and competent to do so.