Worcester Boiler E9 Fault – Error Code Guide

The E9 fault code appears when your boiler has locked out to prevent it from functioning. It can mean that the unit is at risk of overheating, which has the potential to damage internal parts or pose other safety risks.

However, there are other reasons the code may appear, so this guide will help you to understand what may have happened to your boiler and what your next steps are to get it running again.

What Does the Worcester E9 Fault Code Mean?

In Worcester Bosch manuals, the meaning of this code is listed as “Safety temp. limiter in CH (central heating) flow has tripped”.

The safety temperature limiter is a sensor which ensures that the water running through your boiler is not reaching over 105°c, which can lead to damage of internal parts.

These limiters are placed within two of the pipes which leave the unit, the CH flow and CH return pipes.

The E9 code refers to the sensor within the CH flow pipe, which carries heated water away from the boiler into the rest of the house. 

These sensors send signals to the printed circuit board (PCB), which acts as a control centre for the boiler. The PCB must register that each stage of the heating process has taken place safely before it will permit the next stage to begin.

If it receives a signal that the temperature of the flow pipe is too hot, it will ‘lock out’ and display the E9 fault code, preventing the boiler from working until the issue is fixed.

What Causes the Worcester E9 Fault Code?

Along with the E9 fault code on the main display, there will also be a three digit ‘cause code’ to help you and an engineer diagnose the problem.

If this code is not flashing on the display, you should be able to access it by pressing the spanner/return button on your boiler unit, which brings up the information menu.

Fault Safety Temperature Limiter

If this is the issue, you will likely see the 220 or 221 cause code. While it’s possible that the boiler is genuinely overheating, issues with the temperature sensors can also cause false readings to be sent to the PCB.

If the PCB recognises that a sensor is faulty, it will lock out to prevent these faulty readings from occurring.

The most common causes of sensor issues are damaged wiring and water damage. The wiring and connections between the sensor and the PCB can become loose over time due to vibrations within the boiler unit.

If your boiler has been functioning intermittently, this can indicate that the connections are damaged but not entirely severed.

Water damage to the safety temperature limiters can come from any internal leak, and as they are small components it doesn’t take much moisture to interfere with their functioning.

As noted above, a cracked heat exchanger is a common culprit for boiler leaks.

Faulty Heat Exchanger

The 219 cause code indicates that the heat exchanger isn’t functioning as it should. This is the part of your boiler which transfers heat from fuel into water.

A frequent cause of the exchanger overheating is a build up of limescale, which is made up of mineral deposits that enter your home from the mains supply.

This is most common in areas with ‘hard’ water, and with older boilers that have not had filters added to prevent limescale building up.

Areas with limescale burn hotter than others, which can affect the temperature readings taken in the area surrounding the heat exchanger, even if there’s only a small patch.

It’s important to deal with limescale at the earliest sign, as it can irreparably crack the heat exchanger if left unchecked, which leads to leaks.

Faulty or Blocked Boiler Pump

Once water is at the required temperature, the pump pushes it out of the boiler unit and into the house’s pipes.

If it is not functioning correctly, the heat exchanger will be continuing to produce hot water with nowhere for it to go, eventually leading to overheating.

If you have recently had a new pump or boiler installed, it may just be at the wrong setting, as modern pumps have different speeds.

In older boilers it’s more likely that the pump’s moving parts have become worn down through wear and tear, or blocked with heating sludge.

Heating sludge forms as water travels through a heating system and gradually collects tiny bits of rust that flake off pipes.

This turns into a thick mixture which can clog various parts of the boiler.

Damaged Printed Circuit Board (PCB)

As the PCB controls every stage of the heating process, any damage to it will cause the boiler to cease functioning.

The E9 fault code could indicate that connections to the temperature sensors have come loose or been damaged on the PCB, rather than at the sensors themselves.

The most common cause for this is an internal leak, as even tiny amounts of moisture are enough to damage the PCB. 

Since the PCB controls which fault codes are displayed, if it isn’t functioning correctly it may also display inaccurate codes. 

Can I Fix my Own Worcester Boiler with the E9 Fault Code?

The E9 fault code means that your boiler is at risk of overheating if it is forced to run, so you shouldn’t reset it.

This isn’t just a safety measure to prevent gas leaks and explosions, it also protects the components within your boiler.

Overheating can cause damage to expensive internal parts, so it is usually more cost effective to call an engineer straight away anyway.

It’s also important to note that any work required within the unit must legally be carried out by a registered Gas Safe engineer.

How to Fix a Worcester E9 Fault Code

If the Safety Temperature Limiter is Faulty

If loose wiring or damaged connections have affected the sensor, an engineer will probably be able to remove the affected components and rewire them appropriately.

This won’t require costly parts. However, if your engineer may want to check other components to ensure they’re not creating more vibrations than they should, which could incur further repair work.

Water damage to the sensor will require a replacement part. Again, the part itself is not expensive, but your engineer will need to find the source of the leak and conduct any necessary repairs.

If the Boiler’s Heat Exchanger is Faulty

The limescale build-ups common to this component can sometimes be dealt with without a total replacement.

If there isn’t irreparable damage to the exchanger, an engineer may be able to conduct a flush through the whole heating system.

This involves sending specialist chemicals throughout the pipes which dissolve limescale.

However, it is often the case that by the time a fault code has been displayed, the heat exchanger has been damaged and will need to be replaced to prevent leaks.

This is one of the most expensive parts, with £500 not being an uncommon price.

To prevent future limescale issues, your engineer should install a magnetic filter which collects up debris as it moves through the boiler.

If the Boiler’s Pump is Faulty or Blocked

It will be simple for your engineer to reset the pump to the correct speed if that’s the issue, so you will likely only need to pay the call-out fee.

If heating sludge has blocked the pump, your engineer will be able to run a flush through the system. This is a similar process to removing limescale, but the chemicals used are different.

If the pump hasn’t been damaged by the sludge, it can be cleaned and replaced. You should then have a filter added to prevent future build-ups.

Faults that have occurred through wear and tear to the pump’s parts may be repairable, but it’s not uncommon that the whole part will need to be replaced at this stage.

The price for this will depend on your boiler’s model, though somewhere between £150-300 is likely.

If the Printed Circuit Board (PCB) is Damaged

If the issue is loose connections from the PCB, an engineer may be able to rectify the issue without replacing the part. However, if there is water damage to the component then a replacement will be necessary.

Unfortunately, the PCB is the most expensive part of the boiler, frequently costing in the region of £500.

This is one of the reasons why it’s a good idea to address internal leaks immediately, rather than resetting the boiler and forcing it to work despite a fault code being displayed.

Which Worcester Models Use the E9 Fault Code?

Worcester Bosch boilers use a variety of fault and cause codes across their range, but each combination is only used once.

Therefore, no matter which model it appears on, the E9 fault code always refers to an issue with the safety temperature limiter.

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