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Ideal Boiler FH Fault – Error Code Guide

If your boiler’s display screen is showing an alternating F and H, an internal error has occurred that must be addressed before it will begin working again.

You may be able to work out the cause and appropriate fixes at home, though any work inside the boiler unit must legally be carried out by a registered Gas Safe engineer.

This guide will help you to understand the error code, and what your next steps to getting it fixed might be.

What Does the FH Error Code Mean?

Ideal lists the simplified meaning of this code as ‘Flame detection error’. This means that your boiler is unable to confirm when it has successfully lit the flame needed to produce heat.

Within the unit there is a printed circuit board (PCB) which acts as a hub for all of the components that keep the boiler running.

If the PCB is unable to confirm that each step in the process needed to produce heat has taken place, it will cause a short circuit, stopping the boiler from running.

In the case of the FH fault, this is a safety measure to prevent the releasing of gas without a flame being lit, which could lead to a dangerous leak or an explosion.

What Causes the FH Error Code?

While Ideal advises that the flame detection electrode or PCB are likely to be at fault, there are a few other instances which can cause the FH error.

In some instances you may be able to address the issue yourself, but in most an engineer will be required. 

The Boiler’s Flame Detection Electrode is Dirty

This is the component of your boiler which senses whether a flame has been lit, and may also be referred to as its flame sensor.

Over time, this electrode can become blocked due its frequent exposure to the open flame.

The most common culprit is deposits of carbon, but dust and other particles can also cause the sensor to fail. Due to the small amounts of water vapour within the boiler, it may also become rusted.

The Boiler’s Flame Detection Electrode is Damaged

If the electrode has previously been cleaned with too abrasive a material, such as sandpaper, it may have become scratched.

Once the surface is scratched, the electrode becomes more susceptible to failing in the future, as it is more exposed to contaminated combustion air.

The electrode is usually insulated with porcelain, which can also become cracked or broken over time.

The Printed Circuit Board (PCB) is Faulty

If the flame sensing electrode is in working order, it may be that its corresponding terminal on the PCB is not functioning correctly.

As all processes go through the PCB, any failure that affects it will also affect each other part of the boiler’s running, leading to fault codes such as this one.

The Boiler isn’t Receiving Enough Gas

While this code may appear when there is a flame but it’s not being detected, it can also appear if there is something stopping a flame from appearing at the strength needed for the sensor to detect it.

This is likely to be the case if your gas supply has been disconnected, or your pre-paid gas meter isn’t topped up. 

It could also be the case that your gas is connected, but is reaching the boiler at a pressure too low for it to run.

The Condensate Pipe is Frozen

While this isn’t directly related to the flame sensing electrode, it is a common issue which causes error codes with boilers, most often in the winter.

It therefore makes sense to account for the issue if the fault code has appeared during cold weather, as it is a comparatively simple problem to fix. 

All boilers installed in the UK after 2005 must legally use condensing technology, which increases energy efficiency.

This means that the harmful exhaust gases created during the heating process are not wasted, as the unit draws out the water vapour from these gases, reusing them to heat further water.

The wastewater created in this process is acidic, so it must be conveyed safely away from your property. This is done via the “condensate pipe”, which is made of plastic and runs from your boiler to the outside of your home.

At its exit point, it’s exposed to the open air, so in cold weather it can become blocked with ice. 

As the removal of the wastewater is a vital part of the safe running of your boiler, when it senses that this avenue has been blocked, it will cease to function.

Can I Fix My Own Boiler with the FH Error Code?

As this code is likely to point to an issue within the boiler unit, you will need to call a registered Gas Safe engineer in most cases.

There are some steps you can attempt before doing so, all of which do not require interference with the internal processes of your boiler.

If the Boiler isn’t Receiving Enough Gas

  • Top up your pre-paid gas meter
  • Contact your gas supplier to check that your supply hasn’t been cut off due to non-payment or local works
    Check the valve which controls your mains gas supply, ensure that the lever is parallel to the pipe. If it is perpendicular then the supply has been shut off
  • If the valve that controls gas supply to your boiler specifically is visible outside of the unit itself, check that this lever is also parallel to the pipe
  • Check whether other gas-fuelled appliances are working

If the Condensate Pipe is Frozen

  • Find the exit point of the pipe on the outside of your property. They have often been installed at a steep diagonal angle towards a drain
  • Check for visible icy blockages, if the pipe feels very cold to the touch then there may be blockages further in
  • Pour warm water over the pipe to thaw it, or use a hot water bottle to decrease spillage and keep the area safe
  • Do not use boiling water, as this can damage the plastic of the pipe

When Do I Need to Call an Engineer for the FH Error Code?

In the following instances, a Gas Safe engineer will need to diagnose and correct the issue.

If your boiler is under warranty, this service may be included. Otherwise, you may need to pay for replacement parts on top of the labour costs.

The Boiler’s Flame Detection Electrode is Dirty

If this is the issue, an engineer will be able to remove the electrode and clean it gently using emery cloth or steel wool.

They will not need to replace the electrode if it appears to be in good working condition once cleaned, and the boiler returns to full functioning.

This is a process which should also be a part of the regular maintenance check-ups to your boiler.

The boiler’s Flame Detection Electrode is Damaged

If the engineer can clearly see that the electrode or its casing is damaged, they will install a replacement. If it isn’t clear, they should clean the component first before suggesting a replacement, as a new part may not be needed. Flame detection electrodes for the boilers which use this error code cost between £20 and £30 pounds.

The Printed Circuit Board (PCB) is Faulty

After the electrode has been serviced, the PCB and the wiring that it relies upon will be checked over for any damage.

As it’s one of the most expensive parts, a new PCB for Ideal boilers that use this code can cost up to £200, though often engineers are able to order them for much less.

The Boiler isn’t Receiving Enough Gas

If the interruption to appropriate gas supply hasn’t been caused by a payment issue and the valves you have checked appear to be turned on or you are unable to locate them, an engineer can help.

They will be able to service the valves at the mains supply level, as well as those that control the flow into the boiler itself. 

If the issue is low gas pressure, the solutions vary greatly depending on the cause. An example of a simple fix would be insulating the outdoor gas meter, in the instance that cold weather has caused it to frost over and produce incorrect readings that affect the supply.

Which Ideal Models use the FH Error Code?

Newer models in Ideal’s range are less likely to use this code, so if the fault is arising then it’s likely your boiler was manufactured and installed in the early to mid 2000s.

These are some examples of the most common models that may show the FH error code:

  • Ideal Icos HE12
  • Ideal Icos HE15
  • Ideal Icos HE18
  • Ideal Icos HE24
  • Ideal Isar HE24
  • Ideal Isar HE30
  • Ideal Isar HE35
  • Ideal Istor HE260
  • Ideal Istor HE325

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