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Ideal Boiler L9 Fault – Error Code Guide

If your Ideal boiler has stopped functioning and is displaying ‘L9’, your next steps will depend on which model you have, as the meaning has changed over the years.

This guide will help you to establish why the L9 code might be showing, and what action you’ll need to take to rectify the issue.

What Does the L9 Error Mean?

In older models, L9 means that the heat exchanger has overheated.

The heat exchanger is the component of your boiler that enables the hot gases to heat water, without the two mixing.

It’s dangerous for the unit to run at too hot a temperature, so the boiler will stop functioning if it detects that this has occurred.

In newer models, this code means that the PCB (Printed Circuit Board) is unconfigured, or has a fault. The PCB is the centre for all of the electrical operations needed to keep the boiler running.

Each step in the heating process is confirmed with the PCB before it will permit the next to take place.

If it is unable to perform this function, the other necessary steps can’t take place either.

What Causes the L9 Error?

The Heat Exchanger is Blocked or Damaged

Cool water must be able to flow freely to the heat exchanger for it to safely raise its temperature before it circulates around the house.

Two common causes of blockage to this process are limescale and heating sludge, both of which can build up naturally over sustained boiler usage.

Limescale is a chalky deposit of minerals which can be left behind where water has flowed, particularly if that water is considered “moderate” or “hard”.

When a limescale build up on the heat exchanger is prohibiting water from flowing safely, you may hear a whistling sound coming from the unit, which is referred to as “kettling”.

Limescale can cause serious damage to the boiler’s components, so this issue must be dealt with promptly.

Central heating sludge is a by-product of the heating process, so unlike limescale it comes from inside the house.

It occurs when little bits of rust and dirt flake away from the pipes and radiators, collecting to form a thick mixture that may block parts of the system.

Your boiler has a filter to prevent this, but if it isn’t cleaned regularly then it may overflow and thus cease to function.

If sludge is causing your boiler’s problems, you may hear tapping or scratching sounds as bits of rust attempt to travel through the system.

Sustained exposure to limescale or sludge can lead to a cracked heat exchanger, which in turn may cause a leak which will damage other components inside the boiler unit too.

The Water Pressure is Not at the Correct Level

Water pressure that drops continuously is a common sign of a leak caused by a cracked heat exchanger.

The pressure gauge bases its reading on how much water is contained in the system, so if any is being lost through a crack in the heat exchanger, the boiler will struggle to fill up with enough water to meet the required pressure. 

There is a Fault with the System Pump

The system pump is the part of your heating system that pushes hot water around the house, and returns excess water to the boiler to be reheated.

In conventional boilers, it is usually located outside of the unit, either close to the boiler or the water tank. The pumps for combi boilers are likely to be inside the unit or very close by.

This pump may become stuck or seized, which interrupts the safe flow of water at the recommended pressure. If this causes hot water to build up in the unit without anywhere to run to, this can cause the heat exchanger to overheat. 

The PCB has been Installed Incorrectly

If you have had a new boiler installed, or the PCB replaced on your existing boiler, it could have been hooked up incorrectly in a number of ways.

For example, it could be that certain connections can’t be made, leading to an incomplete circuit.

This fault is likely to become apparent very soon after the work has taken place, as the boiler will be unable to function without a correctly installed PCB. Very rarely, an engineer may have fitted an incompatible PCB by accident.

There is a Fault with the Boiler Chip Card

The PCB component itself is often generic, which means it is compatible with boilers of more than one type. In order for it to work with your specific model, a boiler chip card (BCC) is required.

Without a correctly installed BCC, the boiler unit will not recognise the PCB, and since this is needed for it to function, it will be unable to do its job.

A good analogy for this is an organ transplant, where both the organ and the new body must be corrected matched up, otherwise the organ will be rejected.

Common faults with the BCC include incorrect installation and becoming loose due to vibrations in the boiler, but the component may also cease to function over time.

Can I Fix my Own Boiler with an L9 Error?

As the L9 fault code indicates an issue with one of the boiler’s internal components, there aren’t many steps you can try at home legally and safely.

You can always try to reset your Ideal boiler using the control panel on the front of the unit, but the reality is that by the time a fault code shows, the boiler has identified an issue that will continue to stop its proper functioning.

By manually resetting it, you may risk forcing it to run at unsafe temperatures or pressures, which can cause leaks and even explosions.

How Will a Gas Safe Engineer Fix an L9 Error?

When the Heat Exchanger is Blocked or Damaged

If the component is blocked by limescale or heating sludge, your plumber will perform a flush of the system to remove it.

This involves flushing water and commercial cleaning products through the system to dissolve the blockage or force it to leave the system.

They may opt for a power flush, which uses high pressure, or a chemical flush, which relies on the products being introduced. 

The cost for this procedure will vary depending on how many radiators you have in the house, but an approximate price for a house with 6 radiators is £300.

It’s recommended that your boiler receives this treatment once every 5 years as a preventative measure. In the long term, this will save you money by making your home more energy-efficient, and increasing the lifespan of your boiler.

If the heat exchanger is damaged beyond repair, as is often the case with limescale build-up that has gone unchecked, the engineer will need to fit a new one.

An average cost for this service including labour is £500, as this component is one of the most expensive within the boiler.

The Water Pressure is Not At the Correct Level

If this is caused by a leak from a cracked heat exchanger, an engineer will need to replace the component.

If this is not the case, they will diagnose the source of the leak or impediment to regular pressure.

The costs and time required to do so will vary greatly, depending on the parts that need to be replaced or repaired.

There is a Fault With the System Pump

The engineer will check whether the pump has become stuck in some way or is totally broken.

If there is a blockage that can easily be removed, the repair costs will be relatively low.

In the case that a full replacement is needed, the cost for labour and parts can range from £150-350, though this will depend on the model of your boiler.

The PCB has Been Installed Incorrectly

If there has been recent work on your boiler, or a new one fitted, you can call the same person back to address this issue.

They will be able to tell where their installation has failed, and correct it swiftly. 

There is a Fault with the Boiler Chip Card

If the BCC has been recently installed, the same engineer will be able to correct any errors they may have made during the process.

In the case that it has worked itself loose, they can reset it to the right place, but they will also need to inspect the rest of the boiler for any loose wiring or damaged connections that have been similarly affected by the unit’s movements.

If it is simply broken, they will replace the part, which retails at under £50 in most cases.

Which Ideal Models Use the L9 Error Code?

If you have one of these boilers, the L9 code refers to an overheated heat exchanger:

Ideal Icos

  • HE12
  • HE15
  • HE18
  • HE24

Ideal Isar

  • HE24
  • HE30
  • HE35

Ideal Istor

  • HE260
  • HE325

If you have one of the following models, the L9 code refers to an unconfigured PCB:

Ideal Logic MAX HEAT 

  • H12
  • H15
  • H18
  • H24

Ideal Logic MAX SYSTEM

  • S15
  • S18
  • S24
  • S30

Ideal Logic + SYSTEM

  • S15
  • S18
  • S24
  • S30

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