How To Fix Ideal Boiler Showing FU Fault Code
As boilers get older, they start to experience more problems and become inefficient, therefore, if you are getting the Ideal Fu Fault code, our guide can help you.
The Ideal Logic boiler will lock out because of the FU fault code, but this is standard to protect you and your boiler as a boiler lockout means you can’t use the boiler until a Gas Safe registered engineer has repaired it.
This article will answer all your questions about a FU fault on Ideal Logic Boilers and get you out of that dreaded lockout and consider that if you have an old inefficient boiler it may be more cost-effective to get a replacement.
What does the FU Fault code mean?
This FU fault code is listed in an Ideal manual as “Diff greater than 50degC”.
This indicates that your boiler’s return and flow pipe temperatures are more than 50 degrees Celsius apart.
The flow pipe heats water in your Ideal boiler and sends it to your home, and the return pipe brings the water back to the boiler to be reheated.
Parts called thermistors then take a resistance reading of the pipes. These readings are sent back to the PCB, which can then use them to test the pipes’ temperature.
If the PCB is given a temperature reading outside its acceptable range, it will lock out and display a fault code like fu.
This prevents damage to the boiler’s parts if the boiler continues heating but there is no water in the pipes.
It could cause heat damage to internal components like the heat exchanger or system pump.
Your boiler should display the FU code if it is not showing any damage; however, if your Ideal Logic boiler is over ten years old, we suggest considering a new one.
Why not check out our best combi boiler guide just in case you fancy a change in boiler brand?
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What causes the Ideal FU Fault code?
Is the boiler Pump Blocked or Faulty?
The central heating pump controls water flow through your boiler and home.
It can become blocked or stop working; water won’t flow through the return and flow pipes at the right speed. This can lead to temperature differences.
Over time, the moving parts of your pump can become stuck or wear down. This is more common if you have an older boiler.
The pump is also quite common to get blocked with heating sludge.
This slimy substance travels slowly through the system and is formed from rusty flakes and other debris.
If heating sludge is clogging your pipes, you might hear a clanging sound or tapping.
Air can also block the pump, known as “air locking”. This can happen if the boiler has been topped up recently or there are small leaks within the heating system.
The boiler Heat Exchanger is Faulty, Blocked, or Leaking.
It can also be blocked by heating sludge. However, it is more susceptible to limescale buildup.
Limescale, a buildup of mineral deposits that enters your home via the mains water supply, is more common in areas with hard water.
Limescale can build up on parts like heat exchangers and cause them to become extremely hard. This can cause pressure to build up on the heat exchanger, eventually leading to cracking that allows water to escape.
Thermistors Faulty or Incorrectly Installed
The thermistors send readings to the PCB, which it uses to determine the flow and return pipes’ temperature.
A flow thermistor fault could send an incorrect signal or none to the PCB. This could be caused by a fault in the initial installation or wear and tear, which is not unusual for small parts.
Fault with the Printed Circuit Board (PCB).
Your boiler’s central hub is the printed circuit board. The PCB is the central hub of all electronic operations within your boiler. It can confirm that each stage of the heating process has occurred correctly.
It will lock the boiler with the Fault Code if the PCB is unable to verify temperature readings from thermistors.
Also, it is worth noting that the PCB determines fault codes, and can become damaged, leading to incorrect codes.
Dislodged wiring or connections can cause the part to stop functioning completely.
How do I fix my own Ideal boiler showing FU error?
The FU fault code is a signal that there are issues with your boiler’s internal components. There are not many DIY fixes you can safely and legally attempt.
You can try to reset your boiler before calling a Gas Safe engineer to check if the code is cleared.
However, if the code continues to display intermittently, then you should not keep trying to reset it again, as it could cause further damage.
Turn the knob at the front of an Ideal Logic boiler to the ‘Reset” position.
How to Fix the Fault in the FU
You will need a Gas Safe Registered engineer to resolve the problem because it is internal to your boiler. It is illegal to amend a gas boiler or any other gas appliance if you are not qualified.
If your Boiler Pump is Faulty or Blocked
The Gas Safe registered engineer will check to ensure there aren’t any obstructions in the pump. The engineer will remove any air from the pump by “bleeding” it, much like you would bleed radiators.
A new pump is not required. However, if an airlock occurs after you have repressurised the boiler, they might want to ensure there aren’t any ongoing pressure issues.
Heating sludge can cause the pump to become blocked. An engineer should be able to remove and clean it without replacing it.
However, they will have to remove the heating sludge from the system to prevent future blockages.
They will then perform a “flush”, which is the sending of special chemicals through all your house’s pipes. These chemicals are called central heating inhibitors. They will completely dissolve the sludge.
Installing a magnetic filter can help prevent future buildup. This magnetic filter will capture any rust particles in your system and prevent them from forming together. It can be cleaned each time your boiler is serviced.
Your pump may have stopped working and cannot be repaired or unblocked due to prolonged use. Your engineer will have to replace the part in this instance.
This can lead to costly repairs if your boiler is not within the warranty period. Pumps are often more expensive than £250, depending on the model.
Boiler Heat Exchanger Faulty, Blocked or Leaking
The engineer will perform the same procedure as if the pump were blocked if the heat exchanger becomes clogged with heating sludge.
This involves removing the blockage and flushing the entire system. A new part is unnecessary unless the exchanger has been damaged by the blockage.
Limescale buildup can be treated by a flush. However, your engineer will use chemically designed to dissolve limescale.
This can lead to heat exchanger cracking and/or leaking. The whole system will need to be cleaned.
This is a very expensive part of the boiler, and it costs over £600
If Thermistors Are Faulty or Incorrectly Installed
Your installer or visiting engineer can quickly diagnose and resolve any installation issues.
They will check the readings to see if it is a flow thermistor fault and to verify that they are correct if they suspect a part is defective. They will replace the part if it is not functioning or send inaccurate readings.
The good news is that thermistors are easy to replace, as they typically cost less than £20.
If there is a fault with the printed circuit board (PCB),
Your engineer should perform a series of tests before advising that the PCB has stopped functioning completely.
This will allow you to fix loose wiring between the PCB and other electrical components. The only expense is the cost of new wires.
It can cost around £550 if your engineer has exhausted all other options and decides that the PCB must be replaced.
They may recommend a replacement unit if there are other problems with your boiler.
Which Ideal Logic Models Use FU Fault Codes?
The fault codes used by all models of Ideal Logic are the same.
The FU fault code is used to indicate a difference.
If you have an old Ideal Logic boiler, the best thing to do would be to get a direct replacement.
A brand new boiler is a much more energy efficient, and the likelihood of more issues arising drastically increases with old boilers.
Why not read our new boiler cost guide to see if it is cheaper and more efficient to invest in a new one?