Potterton Boiler Repair in Eltham – Emergency No Heating Breakdown

We received a call from a homeowner in Eltham on a cold January morning. Their Potterton Promax Ultra Combi had stopped firing entirely overnight, leaving the whole house with no heating and only tepid water. The customer had tried resetting the boiler multiple times, but the burner light never came on and the display kept showing an E118 ignition lockout code. On arrival, our engineer confirmed the boiler wasn't even attempting to ignite for central heating demand. The fan was running and the air pressure switch was proving correctly, so the flue system wasn't the issue. A combustion analysis showed no gas was reaching the burner, despite the gas valve receiving a supply. The fault pointed towards the printed circuit board, which wasn't outputting the voltage needed to open the gas valve and fire the burner. On closer inspection, the PCB showed visible signs of heat damage around the relay that controls the gas valve — a common failure point on older Potterton Promax units. The board had simply given up after years of use.

Our Gas Safe engineer isolated the boiler electrically and shut off the gas supply before removing the casing. After confirming the PCB fault with a multimeter — no switched live output to the gas valve on heating demand — we removed the old board and fitted a genuine Potterton replacement PCB (part number 5112742). Once the new PCB was fitted, we reconfigured the dip switches to match the boiler model and kW output rating, which is critical on the Promax Ultra to ensure correct modulation. We then carried out a full combustion analysis using our flue gas analyser, adjusting the gas valve to bring CO/CO2 ratios back within the manufacturer's specified range. Finally, we ran the boiler through a full heating cycle, checked the flow and return temperatures, bled the radiators, and confirmed the system pressure was holding steady at 1.2 bar. The boiler fired cleanly and the house was warming up within minutes.