Ideal Boiler FU Fault Code
The Ideal fault code FU temperature differential Q & A or require an engineer for an emergency boiler repair.
The Ideal Boiler Fault Code FU Error Common Q & A
Just below, we have a list of common questions relating to the FU fault code on the Ideal boiler.
- What does the Ideal boiler FU fault code mean?
- Is a boiler showing the FU fault code dangerous?
- What can cause the FU fault code to be displayed on my Ideal boiler?
- How can the pump affect the boiler’s circulation?
- How can I tell if it’s the pump that’s causing the FU fault code to be displayed?
- How can the pump be fixed to clear the FU fault code on my Ideal boiler?
- Bleeding air from the pump hasn’t fixed the problem, what should my engineer check next?
- What is heating sludge and can it be removed from my boiler’s pump?
- Are there any preventative measures I can put in place to stop the FU fault code occurring again?
- How can the heat exchanger become blocked?
- My boiler engineer has noticed a leak coming from the heat exchanger, has this caused the FU fault code to be displayed?
- Can a leaking heat exchanger be fixed?
- How can the NTC thermistors cause problems leading to the FU fault code being displayed on my Ideal boiler?
- How can NTC thermistors be fixed on my Ideal boiler?
- My boiler engineer thinks that it’s the PCB that’s faulty, is this right?
- How much will it cost to install a new PCB on my Ideal boiler?
What does the Ideal boiler FU fault code mean
The FU fault code on Ideal boilers relates to a temperature differential that is too high between the flow and return.
Typically, this relates to water circulation fault which could be caused by airlocks, blockages, or isolation valves being closed.
Is a boiler showing the FU fault code dangerous
As this isn’t a gas related fault, it’s rarely dangerous. However, your boiler should lock out before showing the fault code to ensure that this is the case.
When a boiler locks out, it will cease to work. The problem needs to be fixed and the boiler reset before the fault code is cleared.
The reason the boiler locks out in this case is to avoid damage to components such as the pump and heat exchanger.
What can cause the FU fault code to be displayed on my Ideal boiler
The problem with fault codes like the FU on Ideal boilers is that they’re generic.
The fault relates to temperature differential more than 50 degrees between the flow and return.
This means that water isn’t being able to circulate correctly throughout the heating system.
And that means that fault finding consists of:
- Inspecting the pump’s operation, and checking for damage/wear
- Checking for air locks in the heating system and pump
- Ensuring the heat exchanger isn’t blocked with debris
- Confirming that the NTC thermistors are providing the printed circuit board (PCB) with the correct readings
How can the pump affect the boiler’s circulation
The pump that’s located in your boiler is what circulates water around the heating system.
If the pump is stuck, blocked or airlocked, it’s ability to circulate water is going to be restricted.
So, whilst water leaves the boiler at the correct temperature, because of the restricted flow it’s coming back to the boiler much slower than it should be.
How can I tell if it’s the pump that’s causing the FU fault code to be displayed
One of the most obvious ways to check if the pump is blocked or airlocked, is to see how hot it’s running. A pump that’s noisy or running to hot is likely to have an air lock or small blockage.
How can the pump be fixed to clear the FU fault code on my Ideal boiler
So, the first thing to check is that the pump isn’t air locked. Your emergency boiler engineer will be able to bleed to pump of air.
Air locks will typically occur if the heating system has small leaks. But, they will also occur if the system has been topped up via the filling loop recently. After a top up, the heating system needs to be bled of air.
Bleeding air from the pump hasn’t fixed the problem, what should my engineer check next
If the pump isn’t airlocked, there’s a chance that central heating sludge is blocking the pump. This is going to restrict water flow in the pump.
And, it’s this restricted flow that’s creating the temperature differential between the flow and return pipes on your boiler.
What is heating sludge and can it be removed from my boiler’s pump
Heating sludge is a combination of minerals and rust (from the inside of radiators and pipework).
Over time this condenses into thick dirty water. The problem is the particles that aren’t broken down into dirty water (small bits of rust, for instance) can get lodged in the heating system, including the pump.
Your heating engineer will need to remove the pump, clean it and reinstall it to remove the blockage.
Are there any preventative measures I can put in place to stop the FU fault code occurring again
After you engineer has cleaned out the heating pump, they can run a hot flush using central heating inhibitor. Inhibitor breaks down heating sludge, and the hot flush will remove it from the heating system.
Once the sludge has been removed, the system needs to be re-dosed with inhibitor. This will consistently break down the sludge. By then fitting a magnetic system filter, the sludge can be caught before it reaches the boiler.
Your boiler engineer will then clean out the filter with each service.
How can the heat exchanger become blocked
Like the pump, the heat exchanger can get blocked with central heating sludge. And the same process (hot flush, inhibitor and a filter) can be used to remove the majority from both the heat exchanger and the whole heating system.
However, it’s more common that heat exchangers become blocked with limescale.
This is likely the case if you live in a hard water area. Hard water areas have water with high mineral content, and this is what settles on the heat exchanger and blocks it.
Rather than using a central heating inhibitor, your emergency boiler engineer will use a limescale inhibitor (or, in conjunction with heating inhibitor). This focuses on removing limescale specifically, rather than heating sludge.
My boiler engineer has noticed a leak coming from the heat exchanger, has this caused the FU fault code to be displayed
Limescale on heat exchangers is extremely common. Where it builds up, those sections of the heat exchanger will burn hotter than the rest.
It’s likely that this has contributed to a small crack in the heat exchanger, and that’s what is leaking.
Can a leaking heat exchanger be fixed
In general, a boiler engineer is likely to suggest a replacement heat exchanger, rather than a repair.
Heat exchangers on boilers are not particularly cheap. You should expect to pay somewhere in the region of £450-500 for a replacement.
How can the NTC thermistors cause problems leading to the FU fault code being displayed on my Ideal boiler
The NTC thermistors on your boiler provide the PCB with readings in resistance (typically, around 20k ohms when at 20 degrees). The PCB then converts this to a temperature reading to ensure that that the flow and return are at the correct temperature.
In the case of the FU fault code, the boiler’s recognised that this reading is incorrect.
Although the fault could lie with the pump or heat exchanger mentioned above, it could be faulty NTC thermistors.
If the NTC thermistors on your boiler are faulty, the resistance readings will be incorrect, and the boiler is locking out prematurely.
How can NTC thermistors be fixed on my Ideal boiler
Your emergency boiler engineer will be able to test both the flow and return thermistors are first, installed correctly.
If the thermistors are installed correctly, they can then be tested to ensure they’re providing the correct readings.
If one (or both) of the thermistors isn’t giving the correct signals, they’ll need to be replaced.
My boiler engineer thinks that it’s the PCB that’s faulty, is this right
Before assuming the PCB is to blame, it’s worth testing all other components. The PCB isn’t a cheap component to replace.
Your boiler engineer will however, be able to test the PCB to ensure that it’s getting power using a multi-meter.
If it’s not getting power, there are some potential fixes that could salvage the PCB. They should check the boiler chip card is correctly inserted and that there are no visible wires/connections that are loose.
If wiring or connections are loose, this could be causing intermittent signals between the PCB and other electronic components.
Whereby the boiler engineer can 100% confirm the PCB is to blame, it will need to be replaced to clear the FU fault code.
How much will it cost to install a new PCB on my Ideal boiler
The printed circuit board on your Ideal boiler is one of the most expensive parts. You should expect to pay around £500 for a replacement. And, that’s why your boiler engineer needs to be 100% sure that this is the culprit.
If the PCB and other parts need replacing (such as the pump and heat exchanger) and your boiler is old and out of warranty, it would be wise to get a quote for a new boiler. Investing this much cash in an old boiler that is already failing, would be a waste of money.
Other Ideal boiler issues
For more boiler issues regarding the Idea Boiler then please visit the Ideal Boiler Problems And Cures page.