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Boiler PCB Faults


The Printed Circuit Board, or PCB, is literally and figuratively the brains and heart of your modern boiler. Given its vital role as the centrepiece of your central heating and hot water systems, you wouldn’t want anything happening to it. In other words, if it fails, your boiler fails.

Regardless of your boiler model and age, its operation is centred around the PCB, and if the PCB develops any problems, the boiler will struggle to supply hot water and heating to your home. Once you suspect your boiler’s PCB is faulty or damaged, the first thing on your mind will be to call an emergency boiler repair service. But do you know how much it will cost to replace a faulty PCB?

This article will look at the common signs of PCB faults, the various causes of boiler PCB faults, and the cost of replacing a faulty boiler PCB.

What is a boiler PCB?

As earlier said, a boiler PCB is essentially the control centre of your boiler. It is where all the electronic components of your boiler meet and communicate to ensure synchronicity in functioning. The PCB is responsible for synching the operation of all the parts of your boiler, thus keeping the boiler functioning as it should.

Simply put, the PCB monitors pressure, temperatures, and currents in your boiler to ensure they are within working range for the smooth and efficient running of the boiler. If, however, one part is malfunctioning and operating the boiler under such conditions might damage internal components of the boiler or bring harm to people in your home, the PCB initiates a boiler lockout.

For instance, before the pilot light comes on, the PCB conducts a sequence of checks to ascertain that the different parts of the boiler are working. It first sends a signal to the fan to start running to create a change in pressure that will suck out the dangerous gases that will form in the boiler during operation. Once it receives feedback that the fan is operational, it will deem the operation of the boiler to be safe and thus allow the boiler to ignite.

On the other hand, if the PCB detects that the fan is not working, a broken thermistor, or a faulty gas valve, it will instruct the boiler to cease operation and display an error code.

What are the signs of a faulty PCB?

Before we proceed with this section, it is imperative to state that as the PCB is essentially the heart of your boiler, you shouldn’t mess around with it. You’ll be better off considering it as sacred, that is unless you are a certified Gas Safe engineer. Otherwise, you risk putting your boiler out of commission, and we wouldn’t want that happening.

Another thing to note is that as much as it might be tempting to restart your boiler when you find it locked out and displaying an error code, you shouldn’t do it. The fact that your boiler is displaying an error code means that something is wrong. And by restarting it, you’ll be putting a temporary band-aid on a problem that might be running deep.

With that matter settled, let’s proceed and take a look at some of the most common signs of a faulty boiler PCB.

  1. Display panel not lighting up.

If you notice your boiler’s interface is not lighting up, is blank, or is intermittently displaying green, red, or blue lights, chances are, there is a loose connection between the PCB and the interface.

However, remember that some manufacturers have configured the interface to flash if there is a fault, so it might not be a case of loose wires.

To determine if this is a case of faulty PCB, the registered repair engineer will need to open the boiler and investigate if there are any loose connections. They will make the necessary repairs if possible.

  1. Boiler giving off a burning smell

If you’ve been noticing a burning smell coming from your boiler coupled with the intermittent operation, and then all of a sudden, your boiler displays fault codes relating to electronic failures, it is terrible news for you. The only plausible case in this scenario is that your PCB unit was damaged by water leaking from the boiler.

The burning smell often results from moisture dripping onto PCB connections resulting in burnouts. If this is the case, the boiler engineer will first have to isolate and fix the leak. Once that is done, they can then proceed to replace the burnt-out PCB unit.

  1. The PCB showing a memory fault

If you find your boiler’s display panel displaying “memory fault”, it means the boiler’s PCB is not configured correctly. This error is common in newly installed boilers or if you recently had a PCB replacement.

If your boiler is new, you can resolve the issue by entering the associated product code in the user manual. This product code will synchronise the boiler with the PCB, and the error will disappear. However, if you had replaced your boiler’s PCB, the tactic may not work since the boiler engineer would have tested the boiler before leaving.

  1. No power on the display panel of the boiler

If there are no power cuts, but your boiler’s display is blank, it might be an issue of power not reaching your PCB, or the PCB has had its final day. The engineer will open the boiler and analyse its components to determine if this has something to do with a damaged PCB unit.

  1. Fan not starting

The fan in your boiler is vital for venting out dangerous gases via the flue, and the boiler won’t ignite until the PCB ascertains that the fan is running.

Therefore, if the PCB doesn’t recognise that the fan is running, maybe due to miscommunication between the fan, the air pressure switch, and the PCB, the boiler will lockout.

To determine whether a faulty is the cause of the PCB fault, the registered boiler repair engineer will go on an electrical fault-finding, examining the PCB, the fan, and the air pressure switch. Once they find any loose connections and damaged wirings that may be causing the miscommunication, they’ll fix or replace them.

  1. Unresponsive gas valve

As earlier stated, the operating sequence of the PCB starts by confirming the operation of the fan. Once the PCB recognises the fan is running, it will signal the gas valve to open, thus allowing a steady supply of gas to the burner. However, the PCB may not fully relay the communication to the gas valve due to some faulty electrics between the two.

The miscommunication between the PCB and the gas valve will result in the gas valve not opening at all or opening intermittently.  The gas valve may also open, either partially or fully, when it is supposed to be closed, leading the boiler to shut down as it is potentially dangerous to operate under such conditions.

  1. Boiler cutting out before getting to the desired temperature

If you’ve recently noticed your boiler turning off before the water reaches sufficient temperatures, it might be a case of miscommunication with the temperature sensors on the NTC thermistor. For instance, if this thermistor misleads the PCB to think the water has reached sufficient temperatures, the boiler will be switched off.

What are the causes of boiler PCB faults?

Just like anything else (of course, excluding wine), age does a number on boiler PCBs. As time passes, the boiler components are subjected to wear and tear. For instance, after being in use for years, chances are, the PCB in your old boiler has already developed cracks and fractures on its internal structure, causing it to malfunction. In short, the leading cause of PCB faults in old boilers is old age.

However, if your boiler is relatively new, it might be baffling to find it showing the tell-tale signs of a PCB fault. Given that old age is out of the equation, you might be racking your brains wondering what caused it to develop the faults.

Well, PCB faults in fairly new boilers are often attributed to three factors: boiler vibrations, water damage to internal components, and damaged solder joints. The professional boiler engineer will go on a fact-finding mission to determine which one of the three is to blame for your boiler’s faulty PCB unit. Once identified, the engineer will try to fix the issue before repairing or replacing the PCB unit.

In the meantime, let’s take a look at how these three factors can result in boiler PCB faults.

Boiler Vibration

All boilers naturally produce noises and slight vibrations when they are operating. However, boiler vibrations are to blame if you noticed your boiler being noisier than usual before it developed a PCB fault.

The logic is simple. As most boiler components, including the PCB itself, are fragile, excessive vibrations will make the boiler chip and other connections to the PCB loosen or fall off. The vibrations may also damage some of the wirings on the PCB, resulting in boiler PCB faults.

Therefore, it is unsurprising that the boiler repair tradesperson you call to fix a PCB fault will first try to identify and fix the source of the excessive vibrations before fixing the PCB.  In most cases, the origin of the excessive vibrations will be traced back to a faulty pump or fan.

Water damage

Everyone knows that water and electricity don’t mix. And since a PCB is full of electronic components, contact with water is unwelcome as it can spell its doom.

In most cases, PCB units are damaged by water leaks from the heat exchanger or the pump. Cracking of the heat exchanger is usually attributed to old age or limescale buildup. When limescale develops inside the heat exchanger, it creates hot spots that weaken some of its sections. Over time, the weak areas will crack and allow water to leak and drip on the components of the PCB unit.

On the other hand, a pump may start leaking if it is old or subjected to excessive strains. For instance, if the pump is operated at high speeds or has a sludge accumulation, it will be put under high pressures that can easily blow some seals. The torn seals will allow water to leak inside the boiler, damaging the PCB and other electronics.

Weak or damaged solder joints

Naturally, the small electronic components making up the PCB are soldered together. As time passes, the solder may deteriorate and break off, causing the PCB unit to malfunction or break down. Although some damaged solder joints can be fixed on the spot, there is no guarantee that they will hold for long, and there is also the chance that others may break off soon. Replacing the entire PCB unit is, therefore, the better option.

How much will it cost you to replace your boiler’s faulty PCB?

As the PCB is the most expensive component in your boiler, you will have to fork out several hundreds of pounds to replace it. Here, we are looking at anything between £400 and £550. However, this price varies depending on the boiler model and the labour rates in your location.

In a bid to lower your replacement expenditure, you can consider using a refurbished or reconditioned unit. However, the small savings are not worth it, considering the second-hand unit usually has no warranty and can quickly stop working again.

If your boiler is old and out of warranty, it might not be worth investing as much as £500 in replacing its PCB unit, given that it will need other repairs in the near future. As such, it would be wiser to invest in a new energy-efficient boiler rather than waste a fortune patching an old piece.

Therefore, we advise you to engage the help of your boiler repair engineer when weighing the cost difference between repairing and replacing your boiler.

How long will it take to replace a faulty PCB?

A qualified engineer usually takes 1-2 hours to diagnose and fit in a new PCB. However, if the engineer doesn’t have your specific PCB model in stock, you may have to wait longer for them to source it on your behalf.

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