Boiler PCB Faults, Fixes & Costs

What is a Boiler PCB?

A boiler's PCB (Printed Circuit Board) is the central control unit, using power from the mains electricity supply. 

It interacts with the majority of boiler components using sensors such as: 

• Flame detection sensor
• Pressure sensor
• Temperature sensor
• And so on...!

By interpreting signals it gets from these sensors, it sends 100s of outputs to components. 

A couple of examples of these include when it signals the: 

• Gas valve to open or close
• Diverter valve to switch between heating and hot water
• Your boiler's pump to modulate flow rate

All this combined allows your boiler's printed circuit board to control hot water and heating, as well as lockout your boiler if a fault code is present. 

PCB Replacement 

How Long it Takes To Replace a PCB

The process from diagnostic to getting a new printed circuit board fitted is likely to be a 2-4 hour job.

Bear in mind, printed circuit boards aren’t generally stocked by generic heating and plumbing merchants. 

Unless you have a boiler spares company locally that your engineer can pick up the part from, expect a 2-3 day delay on the installation.

PCB Replacement Cost

The cost of a new printed circuit board is likely to be £500-£600. 

Like any repair, there will be a few variables that determine the exact cost, including: 

• Boiler brand and model (and therefore, the cost of the specific PCB you need)
• How long it takes your engineer to diagnose the fault (emergency boiler engineers charge by the hour)
• Complexity of the installation (some boilers are easier to work on than others, cutting labour time and cost)
• The labour rate offered by your repair engineer, this can fluctuate from £40 per hour to upwards of £100 per hour depending on your location and individual company pricing

PCB Replacement vs Boiler Replacement

For boilers sub 10-years old, under warranty or needing a repair costing £50-£200, the most economical option is a repair. 

However, a printed circuit board replacement is well above this figure, costing £500-£600 to replace.

Consider this…

For small-medium properties, the likes of an Ideal Logic+ is going to cost just over £2,200 to install. That comes with a 7-year warranty (10 years on the heat exchanger). 

So, instead of sinking £600 into an old boiler, you’ll have paid nearly 30% of the cost off on day 1 by putting that money towards a new one. 

We only fit units from the best combi boiler brands in the UK. These brands come with a long warranty and during the warranty period, you won’t need to worry about expensive repair bills like this one. 

As an example, the Ideal Logic+ comes with a standard 7-year warranty. The heat exchanger (another hugely expensive part to replace) is covered for 10-years!

And that’s not all... 

With a new boiler comes higher efficiency, which in turn means huge cash savings on your gas bill. 

Check out this graphic from the Energy Saving Trust: 

(Source)

These figures are based on:

• A semi-detached property
• Having a new A-rated boiler fitted
• Using thermostatic radiator valves, room thermostat and programmer (typical in most installations these days)

Even if you have a relatively new boiler that’s D-rated, you should expect annual savings of roughly £180 on your gas bill. And that figure rises as high as £320/yr for those with a G-rated boiler.

You can check exact prices of a new unit with a long warranty by using our clickable boiler quote tool here.

5 Common PCB Faults & Fixes

Not sure if your printed circuit board is faulty?

Whilst not an extensive list, here are 5 of the most common issues that indicate your PCB needs replacing.

1. No Display or No Power

If your LCD display isn’t lighting up, not showing error codes/current status or has no power this may indicate faulty PCB. 

On rare occasions, this could be caused by a bad earth, so ask your Gas Safe engineer to check this before replacing the PCB.

2. Intermittent Operation

A boiler that cycles on and off or resets at random, is usually caused by a malfunctioning PCB. Most likely, it’s misinterpreting signals coming from the array of sensors that are installed in modern boilers. 

This may cause hot water or heating to come on/off at random, or the boiler’s pump to start pumping when it shouldn’t. 

A faulty PCB in this case would likely lead to multiple issues rather than a single one. 

For instance, if your only problem is a fault code showing low water pressure (error code F1 on Ideal boilers), the pressure sensor could be to blame, not the PCB.

A Gas Safe engineer can use a multi-meter to check individual sensors, as well as the PCB.

3. Inconsistent or Incorrect Error Codes

Error codes allow a Gas Safe engineer to shortlist potential culprits causing a boiler to lockout. 

It’s rare you’d see more than 1 fault code at once (unless you’re incredibly unlucky). So, if your boiler is flicking between various fault codes that relate to low water pressure, the boiler not igniting or more, it’s likely the PCB has failed.

Like the other failures, it’s simply misinterpreting signals from the sensors and this is going to mean that to fix this issue, the PCB needs to be replaced.

4. No Response From Boiler Components

If your boiler isn’t displaying a fault code, yet it isn’t kicking into action when you call for hot water or central heating, the printed circuit board is likely to blame.

Once it receives the necessary signals from sensors, it should fire into action, ensuring that the:

• Diverter valve is set to the right position (dependant on whether you’re calling for hot water or heating)
• Gas valve opens and closes to let the right amount of gas into the burner
• Heat pump fires into action to circulate hot water around your system
• The list goes on…!

A quick test using a multi-meter by a Gas Safe repair engineer will determine if the PCB is faulty.

5. Won’t Ignite Even Though Gas Supply is Fine

A boiler that’s not igniting even when the gas supply is fine, is likely due to an ignition problem. 

Possible issues here include: 

• Faulty leads
• Air supply issue (blocked flue or condensate pipe)
• Low gas pressure
• Low water pressure
• PCB failure

If your boiler engineer knows the PCB is working correctly yet the boiler won’t ignite, it’s worth checking out this guide to why boilers won’t ignite.

And if your PCB is to blame, a replacement will fix the issue.

Why Would A Boiler’s PCB Fail?

The most common cause of a PCB failure is simply age.

The typical lifespan of modern boilers is in the region of 10-15 years. Although we’ve ripped out boilers from properties that are much older (20+ years), at this point they’re extremely inefficient. 

It makes sense to get a new and efficient boiler rather than investing into an old and failing appliance. 

Another common killer of printed circuit boards are boiler leaks. Water leaking on boiler components is never going to end well. If your boiler has a leak that’s not fixed, it’s likely you’ll be in the same position 6-18 months down the line, even after a replacement PCB.

Typically, leaks will derive from either the boiler’s pump, or the heat exchanger. 

Pump leaks are relatively easy to fix with a service kit. 

However, if there's a leak coming from the heat exchanger, that’s likely due to a crack. Cracks occur due to excessive wear, or hot spots thanks to limescale build-up. 

Unfortunately, a crack in your heat exchanger is going to cost in excess of £400 to fix; a replacement will be needed. 

Couple that with a £500+ repair cost for your printed circuit board, and it makes much more sense to replace your boiler, rather than to repair it…

For further reading, we’ve written a guide to how long Ideal boilers last here. 

Or if you’d prefer, you can see how much a brand new unit would cost using our clickable boiler quote tool here.