Potterton Boiler E321 Fault Code
The Potterton fault code E321 lockout Q & A or require an engineer for an emergency boiler repair.
The Potterton Boiler Fault Code E321 Error Common Q & A
Just below, we have a list of common questions relating to the E321 fault code on the Potterton boiler.
- What does the E321 fault code mean on my Potterton boiler?
- Is there a DIY fix for the E321 fault on Potterton boilers?
- Is it likely that my boiler will need to be replaced, or can it be fixed?
- What does the NTC thermistor do on a boiler?
- What causes the E321 fault code to be displayed?
- How can the boiler engineer check the circuit and NTC thermistor, to see if this is the cause of the fault?
- How can air locks cause the E321 fault code to be displayed?
- How does water pressure cause the E321 fault code to be displayed?
- My boiler repair engineer thinks there’s a blockage in the system, how is this caused?
What does the E321 fault code mean on my Potterton boiler
When your boiler has a problem, it will show a fault code on the display panel. It may lock out (i.e. stop working), and this isn’t always a sign that your boiler is completely broken. Generally, this is a safety precaution. The lock out is either protecting components from further damage or isolating a boiler that could pose danger to people in your property.
In the case of the E321 fault code, the lockout is designed to protect the boiler. The problem stems from a heating NTC thermistor fault and is rarely dangerous. As the indication of the problem is vague, there’s a chance of long-term component damage, and the boiler locks out as a precaution.
Is there a DIY fix for the E321 fault on Potterton boilers
Unfortunately, there’s not a DIY fix that will clear the E321 fault code. Only basic fixes such as topping up boiler pressure via the external filling loop should be done by those without experience in fixing boilers.
Is it likely that my boiler will need to be replaced, or can it be fixed
On most occasions, when the E321 fault code is being displayed, the problem can be fixed, rather than a replacement boiler being needed. The only time we’d consider a fitting a new appliance, is when the NTC thermistor, PCB and additional important parts need replacing.
Typically, we find that the problem causing the E321 fault code to be displayed, is most likely to stem from a faulty heating NTC thermistor, or a blockage that’s causing temperature readings to be above or below their tolerance.
Speak to a qualified Gas Safe boiler repair engineer, and they’ll be able to figure out what’s causing the issue.
What does the NTC thermistor do on a boiler
Your boiler is controlled by the printed circuit board (PCB). The PCB gives and receives signals from a range of electronic components in your boiler, including the NTC sensors.
The NTC thermistor will monitor resistance readings. When temperature rises, the resistance reading will fall, and vice-versa. The reading is sent to the PCB, that converts it to a temperature.
By analysing these readings, the PCB can recognise when a boiler’s flow (hot water leaving the boiler) or return (water that’s coming back to the boiler to be re-heated) is too hot/cold.
If there’s a problem leading to the incorrect temperature of flow or return water, the boiler will lock out and display a fault code, such as the E321 code you’re seeing.
What causes the E321 fault code to be displayed
The causes of the E321 fault code can be split into two categories, one being faults directly related to the sensor:
- The NTC thermistor has a short circuit
- It’s faulty
- The wiring to the thermistor from the PCB is damaged or loose
And, other mechanical faults leading to water temperature that’s too high/low:
- A heating system with air locks
- Water pressure that’s too low
- Blockage in the pump or heat exchanger
How can the boiler engineer check the circuit and NTC thermistor, to see if this is the cause of the fault
So, the first thing your engineer needs to do, is determine whether this fault is electrical. Using a multi-meter, they’ll be able to test all aspects the electronics in your boiler. That’s going to include the NTC sensor, all wiring and connections, and even the PCB.
By testing each part of the circuit, they’ll be able to determine if any section of the circuit isn’t getting power. They can then either repair that section of the circuit (for instance, by replacing sections of wiring), or replace the faulty component (for instance, the sensor).
But, if they find that the PCB is to blame, it’s likely they’ll want to assess the condition of your boiler. A PCB can cost upwards of £400 to replace. If other components are also going to need to be replaced soon, it makes sense to purchase a new appliance instead.
How can air locks cause the E321 fault code to be displayed
Not all E321 fault codes, are electronic faults. If your PCB and sensor are both getting power, there’s a chance that there’s a problem within the heating system, that’s hampering its ability to circulate water.
A frequent problem for modern heating systems, is air locks. The most obvious place to start when it’s a hot water sensing issue, is the pump. If the pump is air locked, it’s ability to circulate water is going to be hampered. This might mean a higher than normal flow temperature, and a low than average return temperature.
Bleeding the heating pump, should clear the fault.
How does water pressure cause the E321 fault code to be displayed
Like air locks, a system with low water pressure, isn’t going to allow water to be pumped around the system correctly. Your heating system should be pressurised to around 1.3 bar (check your boiler manual for the exact pressure rating). Typically, if your boiler is below 0.6 bar, it’s going to lock out. But, anything between 0.6-1.3 bar, could be affecting the boiler’s ability to circulate water.
If your boiler pressure is too low, you can top it up, by using the external filling loop. And, if you do overfill the boiler, you can release pressure via the drain cock, or the bleed screws on radiators. Be aware, you’ll hear a slight hissing (air being released, which isn’t a problem), then water will run out of the system. So, make sure walls and floors are protected, and you have a container handy to catch the water.
My boiler repair engineer thinks there’s a blockage in the system, how is this caused
The most probable cause of a blockage is central heating sludge. And, like everything mentioned above, a blockage is going to reduce the boiler’s ability to circulate water. In fact, it can put excess pressure on the pump and even the heat exchanger, causing extensive damage over time.
What you need your boiler repair engineer to do, is to flush out the heating system using central heating inhibitor. If there’s a blockage in the pump or heat exchanger, this is likely to clear it.
But, you need to do more than just clear it, you want to prevent it from happening again. And, the best way to do this is to fit filters, alongside dosing the system with inhibitor.
A magnetic system filter from companies such as BoilerMag, MaganClean or Fernox, will catch heating sludge as it circulates around the system. And, they’re able to do this thanks to the inhibitor. It’s this inhibitor that breaks down the heating sludge into small enough particles for the filter to catch it.
And, if you are in a hard water area (i.e. limescale is a problem), there are companies such as Scalemaster, that produce limescale filters specifically for this reason.
Other Potterton boiler issues
For more boiler issues regarding the Potterton Boiler then please visit the Potterton Boiler Problems And Cures page.