Welcome to our 5-minute guide to boiler PCB fault finding.
This guide is generic, and covers all boiler brands. The operation of a circuit board is similar in every boiler.
So, this covers everything from the old Potterton Suprima, to the old Ideal Isar, and even the newer Worcester Greenstars.
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The PCB (printed circuit board) is the heart of your boiler’s electronic components. All electronic components communicate with the PCB.
For instance, the air pressure switch will send a signal to the circuit board to say the fan is operational (helping to vent gases out the flue), and therefore is safe to ignite.
And, the NTC thermistors communicate with the display panel, to tell the boiler that the differential in temperature between the flow and return pipes is within working range.
It also monitors pressure, temperatures and currents to ensure that the boiler is:
Before we go any further, it’s worth noting that unless you are Gas Safe registered, you shouldn’t be opening a boiler’s casing, or working on it.
Get a professional to come and help you here. And, if you’re not prepared to sink £300-550 into an old and unreliable boiler, you can get a replacement price right now, over at BOXT. They’re part owned by Bosch. So, if it’s a Worcester boiler you want, this is about the cheapest place to get one.
Also, symptoms can easily be misdiagnosed. Most symptoms aren’t limited to one faulty part.
For example. A display panel failure could be a circuit board issue, but it could be an electrical supply issue.
A fault whereby the fan doesn’t work could be a PCB problem, but it could just as easily be the fan.
The boiler interconnects with all electrical components on your boiler, including the display panel.
If you see lights (green, red and blue, depending on your boiler) flickering, this can be a sign of a faulty PCB.
However, don’t confuse this with flashing. Some boilers use flashing as a signal they are in service model, or have a fault.
Burning smells on a boiler that operates sporadically, or failure of a display panel, can mean parts of the circuit board have burnt out.
If there’s no power to the display panel, the PCB could be at fault. The engineer will need to test by checking the PCB has power.
If it does, they’ll then move onto other parts like the fan to determine whether the issue lies with the PCB, or other parts in the boiler.
As the PCB on a boiler effectively controls all internal electrical components, when it fails, they can malfunction.
It will miscommunicate with things like the programmer (causing it to cycle on and off for no reason), or the air pressure switch (and won’t fire up).
Fault finding isn’t necessarily easily. Because, there’s a tonne of the things that can contribute to your circuit board failing.
The best course of action is to have an engineer come and run some electrical tests using a multimeter on your boiler.
To determine the cause, they might look for any of the following.
A killer for electrical components in boilers, is water. This might be a small leak from the pump, or a cracked heat exchanger.
This moisture turns to condensation thanks to the internal temperature of the boiler’s parts, and finds it’s way into electrical components, like the ignition lead and of course, the PCB.
If there are leaks present in the boiler, they need to be found and fixed, before replacing the circuit board.
Cracks and fractures on the PCB will cause it to malfunction. If it shows signs of either, it’s probably time for a replacement.
The small electronic components that make up your circuit board are soldered together. If this solder deteriorates, breaks off, or gets damaged, the unit will malfunction.
Of course, there is an option to spot weld to repair the PCB. But, the time it takes means it’s much wiser to replace the whole unit.
These units are rarely worth reparing. It’s much better to consider a replacement, especially if your boiler is out of warranty.
The time spent on repairs (and therefore the cost of labour) usually gets close to the cost of the replacement part anyway.
Labour rates across the country vary. Likewise, parts for different boilers vary too.
But, expect to pay anywhere between £300-550 for a replacement PCB.
This price drops if you’re considering a refurbished or reconditioned unit, but again, it’s rarely worth the small cash saving to have a second-hand unit (that has no warranty).
If your boiler is out of warranty and starting to show it’s age, there’s little point investing upwards of £300 in it.
There’s a good chance other expensive parts are going to let-go in the not to distant future.
It’s worth weighing up the cost differential between a repair and a replacement when the engineer arrives. Or, you can check the exact price you’ll pay for a Worcester Bosch installation here.
Depending on the complexity of the boiler, it should take 2-3 hours for a diagnostic and fitting.
Need help with your boiler’s circuit board? Get professional help here.
And, thanks for reading our 5-minute guide on faulty boiler PCBs.
Still got questions? Leave a comment below and we’ll get back to you as soon as possible.