Potterton Boiler E20 Fault Code


The Potterton fault code E20 NTC thermistor Q & A or require an engineer for an emergency boiler repair.


The Potterton Boiler Fault Code E20 Error Common Q & A


Just below, we have a list of common questions relating to the E20 fault code on the Potterton boiler.

Potterton Boiler E20 Fault Code

  • What does the E20 fault code mean on my Potterton boiler?
  • What are the NTC thermistors in my Potterton boiler?
  • Is a boiler with an NTC thermistor fault dangerous?
  • If my boiler is showing the E20 fault code, will it need to be replaced?
  • What causes an NTC thermistor fault on Potterton boilers?
  • If the NTC thermistor is all that’s needed to clear the E20 fault code, how much is a replacement?
  • Besides a faulty thermistor, is there anything else that could be causing the problem?
  • My boiler engineer thinks the issue lies with the resistance readings the NTC thermistors are logging, could that be right?
  • How would limescale overheat the heat exchanger?
  • If the pump is faulty, what happens to the NTC thermistor readings?
  • My boiler engineer has not found any problems with any of the above, what could be the problem?
  • The wiring and connections to the PCB are fine, what’s the next thing to check?
  • My boiler repair engineer thinks the best option is to replace the PCB, how much is this going to cost?

What does the E20 fault code mean on my Potterton boiler


The E20 fault code on a Potterton boiler relates to an NTC thermistor fault.

Your boiler is controlled by a central unit, called a printed circuit board (PCB). The PCB doesn’t just give signals for other electronic parts to operate. It also receives signals from a range of sensors in the boiler.

These include water pressure sensors, air pressure sensors, and the NTC thermistors.

What are the NTC thermistors in my Potterton boiler


NTC thermistors log readings in resistance on the flow and return pipes of your boiler. The flow is the pipe allowing hot water to leave the boiler. The return is the pipe that allows water to re-enter the boiler ready to be re-heated, after it has circulated around the heating system.

These thermistors don’t log a temperature reading. Instead, they send their resistance reading to the PCB, which then converts this reading to degrees. As heat goes up, the resistance reading goes down.

The idea behind the NTC thermistors as a monitoring device is a safeguard. They help the PCB to determine things such as:

  • Flow temperature isn’t increasing after start up
  • Maximum temperature differential between the flow and return temperature has been reached
  • The flow and return readings are reversed

Like all other sensors in your boiler, the NTC thermistors help the PCB to determine whether the boiler is operating correctly.

Is a boiler with an NTC thermistor fault dangerous


Typically, a boiler with an NTC thermistor fault isn’t dangerous. However, that’s not to say you should constantly reset your boiler to try and fix the problem. The reset function on your boiler is designed to be used after the problem has been found and fixed; it’s not a cure.

It’s likely your boiler has locked out after displaying the E20 fault code. This is either to stop the boiler from operating dangerously (unlikely, in this case), or to protect important boiler components.

Many faults can lead to boiler components being damaged. So, a lock out isn’t just an indication of a fault that needs to be fixed, it’s a safeguard to protect you from further expensive repair bills.

If my boiler is showing the E20 fault code, will it need to be replaced


If the fault lies with the NTC thermistor, and not the PCB, it’s unlikely your boiler will need to be replaced. Typically, the E20 fault code can be fixed for less than £150.

What causes an NTC thermistor fault on Potterton boilers


The first and most obvious thing to check here, is the NTC thermistor itself. They are small and fragile parts and like any part on a boiler, they can deteriorate over time.

Your boiler engineer will be able to quickly and easily test the NTC thermistor on both the flow and return. Typically, they’ll be analysing the thermistor using a multi-meter. That helps them to determine that the unit is getting power.

Once they’ve determined that the unit is getting power, they’ll want to test resistance. Each model of Potterton boiler is different, but they’ll expect to see around 12K ohms @ 20C. If this isn’t the case, there’s a good chance that the thermistor they are monitoring will need to be replaced.

If the NTC thermistor is all that’s needed to clear the E20 fault code, how much is a replacement


Thermistor replacements, in terms of boiler repairs, are relatively inexpensive. A fix here could be in the region of £100-150.

However, your boiler engineer will need to check what’s caused the issue in the first place. There’s little point making a repair if the root cause of the problem (a leak, for instance) is still present.

Besides a faulty thermistor, is there anything else that could be causing the problem


Once you call a Gas Safe engineer, they won’t just check the thermistor. They’ll want to isolate the problem and that means checking all wires and connections.

Boilers vibrate, and these vibrations can easily work fragile parts like thermistors loose, as well as their wires and connections. If even one wire or connection becomes lose, the signals being passed to and from the PCB are going to be intermittent.

If this is the case, you’ll notice your boiler acting strangely. For instance, it might cycle on and off, and not ever getting heating/hot water up to temperature.

Typically, loose wires and connections can simply be re-secured to fix the fault.

My boiler engineer thinks the issue lies with the resistance readings the NTC thermistors are logging, could that be right


The fault here doesn’t necessarily lie with a faulty NTC thermistor, it could be the temperature that these thermistors are logging. Typical issues that will cause a boiler to lock out include a heat exchanger overheat.

When a heat exchanger overheats there are usually two culprits. The first is limescale build-up on the component. The other is a faulty pump. Each will lead to flow water being too high in temperature.

How would limescale overheat the heat exchanger


Limescale is a big problem with all types of boilers. It comes from mineral deposits in water. And, when these minerals settle on boiler components, they can cause all sorts of problems. Typically, we find that any part these minerals settle on will overheat.

For the heat exchanger, that means it burns hotter than it should, and that’s going to lead to the NTC thermistor on the flow monitoring a temperature reading that’s too high.

But the bigger problem here, is a heat exchanger with limescale build-up on it, can lead to cracks. These cracks cause leaks. Not only will the heat exchanger need to be replaced at a cost of around £450, the leak could cause water damage to other parts.

If the pump is faulty, what happens to the NTC thermistor readings


If your pump is partially seized, blocked with debris, faulty, or on the wrong speed setting, it won’t be producing the water flow that it should. This means that water sits in the heat exchanger for too long and overheats.

Once in the heating system, water circulates slowly. The longer it takes to circulate the full length of the heating system, the more temperature it loses. Eventually, this is going to mean that the maximum temperature differential between the flow and return thermistor is reached, and the boiler will lock out.

So, if the boiler engineer has checked everything else, they’ll want to check the operation of the pump too.

My boiler engineer has not found any problems with any of the above, what could be the problem


As with any problem that involves electrical boiler components or fault codes, the PCB needs to be ruled out as the culprit. This is simply since the boiler’s PCB controls all electronic components. And, it’s this unit that displays fault codes. So, it stands to reason that if there’s a fault with the PCB, the fault code being displayed could be incorrect, or the PCB could be to blame.

As this fault relates to an NTC thermistor fault, the first check would be the wires and connections that connect the thermistor and PCB. Even the smallest boiler vibrations could have caused these to come loose. If they have, the boiler is going to work intermittently; it won’t be receiving the correct resistance readings from the thermistors.

The wiring and connections to the PCB are fine, what’s the next thing to check


Your boiler engineer will keep tracing the problem back until the fault is found. As they’ve checked the NTC thermistor as well as its wiring and connections, they’ll need to check the PCB next.

Using a multi-meter, they’ll check the PCB for power. If the PCB is showing intermittent readings, there are a few explanations. The first is that the PCB has been exposed to water damage. This water damage could come from a leaking pump, or something such as a leaking heat exchanger, like we mentioned above.

Your boiler repair engineer will need to determine if the PCB is worth saving, or if a replacement would be the most financially viable option.

My boiler repair engineer thinks the best option is to replace the PCB, how much is this going to cost


Replacing a PCB isn’t a decision that should be taken lightly. The cost of a typical replacement sits in the region of £450-500 including parts and labour; the price will vary depending on the exact model Potterton boiler you have.

Before replacing the boiler’s PCB, your engineer will need to assess the overall condition of your boiler. A basic boiler replacement could be as little as £2,000 and come with a 5-year+ warranty. So, if expensive parts such as the gas valve, heat exchanger and pump are likely to need replacing soon, alongside the £500 replacement cost of a PCB, it makes sense to replace the boiler rather than repair it.

Other Potterton boiler issues


For more boiler issues regarding the Potterton Boiler then please visit the Potterton Boiler Problems And Cures page.