Baxi Duo-Tec E20 fault code

Baxi Duo-Tec E20 fault code explained

If you have a Baxi Duo-Tec boiler you may experience the E20 fault code at some point.

The E20 fault code can cause your Baxi Duo-Tec boiler to stop working, leaving you without central heating or hot water.

Baxi Duo-Tec boilers have various sensors, controls and failsafes in place, in order to control the boiler.

The E20 fault code is trying to tell you that the boiler thinks there is an issue with the primary(main) thermistor(sensor) on the boiler.

The primary thermistor communicates with the printed circuit board on the boiler(PCB)

When a primary thermistor fails, it stops providing a reading back to the printed circuit board that controls the boiler.

Because of this the boiler has no means of controlling the boiler temperature and has no choice but to shut down displaying a the E20 fault code.

Unlike a lot of fault codes on Baxi Duo-Tec boilers, the E20 fault code is very specific and is trying to tell you that the printed circuit board(PCB), isn’t getting a reading from the primary thermistor).

A thermistor is a sensor used to detect temperature. All modern boilers use thermistor’s.

A Baxi Duo-Tec boiler has two thermistors(not including the one in the flue).

A Baxi Duo-Tec boiler also has two heat exchangers and needs one thermistor to measure the temperature in each one.

These sensors work using a small voltage and a variable resistance, which alters depending on the temperature of whatever it is they are sensing.

The correct name for these sensors is thermistor, but some people(engineers mostly) like to refer to these as NTC’s.

In the Baxi Duo-Tec installation manual it refers to them as NTC’s as well.

NTC stands for negative temperature coefficient.

A negative temperature coefficient thermistor’s resistance lowers as the temperature of whatever it is sensing rises, hence the name.

You do get such a thing as a positive coefficient thermistor(PTC), but they are used on other applications, not boilers in general.

The primary thermistor on a Baxi Duo-Tec, senses the temperature of the flow pipe water coming straight from the primary heat exchanger.

The second thermistor on a Baxi Duo-Tec boiler is called the domestic hot water thermistor.

The hot water thermistor sensor detects the temperature of the water coming out of the secondary heat exchanger which is going to the hot taps.

If you have an issue with the hot water thermistor you are likely to see the E50 fault code instead of the E20 fault code.

When the primary thermistor on a Baxi Duo-Tec boiler fails completely, the printed circuit board has no way of knowing exactly how hot the boiler is.

As such the printed circuit board has no way of controlling the temperature of the boiler.

Because the printed circuit board has no means of controlling the temperature of the boiler, it has no choice but to shut the boiler down and display the E20 fault code for safety reasons.

When to call a gas engineer to fix your boiler

If you are experiencing the E20 fault code on your Baxi Duo-Tec boiler, it is important to take action as soon as possible.

While some issues can be resolved by homeowners themselves, others require the expertise of a qualified Gas Safe registered heating engineer.

A persistent E20 fault code more than likely means that the primary thermistor sensor on your boiler is not reading properly and is likely to fail completely at some point as they often do.

The E20 fault code is often caused by a faulty thermistor, but could also be caused by a faulty printed circuit board or wiring harness potentially.

This is why it is extremely important to get a suitable heating engineer with experience on Baxi Duo-Tec boilers, otherwise you could end up wasting money fitting expensive parts to your boiler that are unnecessary.

So it usually best to get a qualified Gas Safe registered heating engineer to have a look at your boiler at your earliest convenience.

How to prevent the E20 fault code

A lot of the time certain faults on a Baxi Duo-Tec boiler can be prevented with regular annual servicing and maintenance. This is not generally the case with the E20 fault code.

A lot of the parts on a Baxi Duo-Tec boiler are non serviceable parts, this includes the thermistor’s. This means that there is nothing that can be done to these parts to extend the life of the fan and prevent the E20 fault code.

Whilst thermistor sensors cannot be serviced or repaired, they can be tested to see if they are reading in the right range.

An experienced engineer used to working Baxi Duo-Tec boilers may detect unusual reading on the front display during routine servicing the boiler and suspect the primary sensor is starting to go faulty.

As such they may be able to recommend replacing the thermistor before it fails as a preventative maintenance measure.

This may help to avoid your Baxi Duo-Tec boiler braking down when you need it most – like in the middle of winter.

Baxi Duo-Tec boilers affected by the E20 fault code

The E20 fault code on Baxi Duo-Tec boilers can affect any Duo-Tec combination boiler.

Below is a list of Baxi Duo-Tec combination boilers that can be affected by the E20 fault code;

• Baxi Duo-Tec 24, 28, 33 and 40 combination boilers
• Baxi Duo-Tec 24 GA, 28 GA, 33 GA and 40 GA combination boilers

Frequently asked questions:

Is my boiler showing an E20 fault code worth repairing ?

Yes definitely, most of the time your broken Baxi Duo-Tec boiler displaying an E20 fault code will be worth repairing.

Obviously the cost to repair your boiler will be determined by which parts need to be replaced.

You would need a competent, Gas Safe registered heating engineer to have a look at your Baxi boiler and make an assessment to determine exactly which parts might need to be replaced.

Before replacing your boiler it is always worth getting a suitable Gas Safe registered heating engineer, with experience working on Baxi Duo-Tec boilers, to make an assessment of your boiler so you can determine whether it is worth fixing not.

Can I repair the E20 fault code myself?

Sometimes you can solve an E20 fault code yourself short term by turning your boiler off, letting it cool down and trying to use it again.

This trick won’t work most of the time.

Sometimes it will work though. This is because often thermistor sensors will provide a reading back to the printed circuit board at certain temperatures(usually lower temps), but go open circuit , and provide no reading back to the PCB when they get too hot – shutting the boiler back down again to an E20 fault code.

Aside from what has just been mentioned, repairing the E20 fault code will usually require removing the cover of your Baxi Duo-Tec boiler to replace parts which you are not legally allowed to do unless you are a Gas Safe registered heating engineer.

Is the E20 fault code dangerous?

No, in general the E20 fault code on a Baxi Duo-Tec boilers is not inherently dangerous.

Modern Baxi boilers are designed with fail safes in place to make sure that the boiler will only work if it safe to do so.

If you are having issues with an intermittent E20 fault code, resetting the boiler is often only a short term solution to your problem, and your boiler may stop working altogether at some point.

As such if your boiler is coming up with an E20 fault code, the best thing to do it get it repaired at your earliest convenience, by a suitable Gas Safe registered heating engineer – ideally one that has experience working on Baxi Duo-Tec boilers.