Vaillant ecoTEC Plus - Repairing a Faulty PCB to fix F61 / F62 & other F6n F7n errors.

Work on Gas Boilers must be carried out by competent Gas Safe Engineers. Maybe If your Gas Engineer diagnoses that you need a replacement Printed Circuit Board (PCB), ask him to remove the board and let you find a competent electronics person to change the capacitors?

If you have an ecoTEC Plus series boiler, especially over say 7-8 years old, and it's showing intermittent F.62 F.61 (i.e Valve errors) or other spurious F.6n / F.7n errors and the problem has been diagnosed to a faulty PCB, then it is 95%++ likely these electrolytic capacitors are the cause of your PCB problems.

PCB replacement appears to be extremely common to fix F62 / F61 errors, especially on older Vailant ecoTEC boliers. Currently PCB prices have skyrocketed PLUS it's an environmental disaster to discard thousands of PCBs every year with many PCBs apparently suffering from a VERY common problem which requires just one or two aged electrolytic capacitors to be changed. (C5 & C9 = 470uF/35V - or better).

Electrolytic capacitors are notorious for failing over time with their Capacitance and ESR going significantly out of spec. This leads to noise on the power supply rails, circuit instabilities and inability to accurately measure low level signals. Sometimes these caps may show visual signs of deforming, leaking or bulging - but not always. Capacitor lifetime is shortened by elevated temperatures (ha, its a boiler!) and/or if subjected to high ripple currents or under spec'd.

NOTE - Electrolytic capacitors are polarised. Before removing the old capacitors, make a note of their orientation and make sure you fit the new ones in the correct direction!!

Dig around some old TV/ PC / Printer or other switching power supplies and its highly likely you will find suitable replacement capacitors.

Warning- Leave the PCB unpowered for at least 10mins to let the large high voltage SMPSU capacitor to discharge, then check its terminal volts with DMM before handling the PCB.