The Worcester Bosch range of boilers is extremely popular in homes and businesses alike. However, like any other heating system, it can sometimes experience errors and malfunctions. One of the most common errors homeowners report with a Worcester Bosch boiler is the E5 218 error code.

E5 218 Error code in a Worcester Bosch Boiler.
The E5 218 error code indicates a problem with the flow temperature sensor in the boiler. This sensor monitors the water temperature as it flows through the heating system. If the water temperature fluctuates from its optimal range (too high or too low), the sensor will detect it and activate an E5 218 error code to alert you.

How does the faulty flow sensor indicate the E5 issue?

NTC thermistors are vital sensors for monitoring boilers' flow temperature and water return.
These devices measure resistance in ohms and communicate the readings to the PCB (Printed Circuit Board), which converts the data into a temperature reading. The NTC thermistor on the flow pipe will signal when the water temperature is too high.
To investigate any issues, a Gas Safe engineer can test the NTC thermistor using a multimeter to diagnose the cause. The thermistor can be replaced if required, which will clear the E5 fault code.

When a boiler overheats, what are the effects?

As a homeowner or business owner, it's important to know what happens if your boiler overheats. When this occurs, it may put unnecessary strain on other crucial components within the boiler, such as the heat exchanger. If this vital part starts to boil at a temperature higher than it's designed to withstand, it can weaken and possibly crack the heat exchanger.

In addition, if there are electronic faults that prevent the boiler from locking out, the continued operation will also cause damage to other critical components. Thankfully, modern boilers now have a fail-safe, known as a boiler lockout, to prevent further damage should it overheat.

A boiler displaying an E5 fault code is not inherently dangerous but might be if left. Proactively turning off the boiler until a heating engineer can attend could save further costly boiler repairs. Therefore, by understanding the risks of an overheated boiler, you can help prevent costly repairs and ensure the longevity of your heating system.

There are several possible reasons why the flow temperature sensor may be malfunctioning.

Reasons for faulty flow temperature

Build Up of limescale inside the sensor.
One common cause is the gradual buildup of limescale or other deposits inside the sensor. Over time, these deposits can cause the sensor to become less sensitive and responsive, resulting in false readings and triggering the E5 218 error code.

Limescale buildup may seem like a minor issue, but it can cause a significant impact. When it comes to your central heating system, even the smallest amount of limescale can cause certain areas to burn slightly hotter than the rest. In hard water areas, it’s more likely that limescale will build, which can affect the efficiency of the boiler.

This can be a problem for NTC thermistors, which monitor the temperature of water flowing into and out of the boiler. If there is a limescale near the thermistor, it can cause it to generate the wrong reading, which could then trigger a boiler lockout. While the rest of your system may be functioning normally, keep an eye on any potential limescale buildup to avoid any boiler mishaps.

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What is limescale?
In simple terms, limescale buildup results from minerals found in water. The harder the water, the more concentrated the minerals, which means that areas with harder water are more prone to limescale problems. Limescale buildup can occur in central heating systems, causing blockages and impairing functionality. It can also impact essential boiler components, leading to fault codes such as the E5 218 or E5 332. Unfortunately, once limescale has settled, it's challenging to remove. This is why it's crucial to identify and tackle limescale as soon as possible.

Possible remedies.

1. A powerflush

2. A water softener

3. In-line scale reducers

Faulty sensor or wiring issue
Another possible cause of the E5 218 error code is a faulty sensor or wiring issue. If the sensor itself is faulty or not properly connected to the boiler's control board, it may not accurately detect the temperature of the water flowing through the system.

Can resetting solve the problem?

Sometimes it does.
If your Worcester Bosch boiler shows E5 218 error code, there are several steps to troubleshoot the issue.

Reset your boiler
First, check the boiler user manual for specific instructions on how to reset the error code. Sometimes, resetting the boiler system may be enough to fix the error and restore regular operation.

When your boiler has locked out, it's important to resist the urge to reset it yourself and continue its operation. When resetting, an internal problem could cause damage to the internal components. Even when the issue has been resolved, it may take some time for the boiler to settle and recognise this. During this period, the boiler may continue operating, which could potentially cause further damage. It’s time to book a visit from a Gas Safe engineer, who will be able to assess the situation, fix the problem, and reset the boiler to ensure its safe operation.

Flow temperature sensor wiring issues
If resetting the system does not work, the engineer will thoroughly inspect the flow temperature sensor and wiring for signs of damage or wear. Always, in these circumstances, get help from a professional heating engineer/plumber.

Remember, routine maintenance, inspection and an annual boiler service can help prevent issues from arising.

If you are experiencing the E5 218 error code or any other issues with your Worcester Bosch boiler, be sure to contact serviceteam, who are Worcester Bosch accredited qualified professional installers.


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