Vokera E020 Fault Code: Causes, Fixes & Repair Costs
What does the Vokera E020 fault code mean?
The E020 code means your Vokera boiler has triggered its limit thermostat as a safety response to overheating. When the internal temperature climbs beyond safe operating limits, this thermostat cuts in and shuts the boiler down to prevent damage. E020 is classified as a final fault — the boiler will not restart on its own. You must address the underlying cause and manually reset the unit before it will fire again. A one-off reset is worth trying, but if the code reappears, the boiler is repeatedly overheating and professional investigation is essential.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Poor water circulation due to a failing pump Common
The circulation pump is responsible for moving heated water around your system. If it has seized, is running slowly, or is losing pressure, water stagnates near the heat exchanger and temperatures spike rapidly, tripping the limit thermostat. This is the single most common trigger for E020.
- Sludge or scale restricting water flow Common
Over time, corroded system debris and limescale can accumulate inside the heat exchanger and pipework. This narrows the flow path, slows circulation, and causes localised hot spots that the limit thermostat detects as overheating. Systems without a magnetic filter or inhibitor are particularly vulnerable.
- Air trapped in the system or heat exchanger Sometimes
Air locks prevent water from flowing freely through parts of the system, creating pockets where heat builds up unchecked. This often becomes apparent after recent plumbing work, a pressure loss event, or when radiators feel cold at the top.
- Faulty or degraded limit thermostat Sometimes
Although the E020 code points to the limit thermostat tripping, the component itself can occasionally fail in a way that causes false readings — shutting the boiler down even when temperatures are within normal range. A Gas Safe engineer can test the thermostat directly to rule this out.
- PCB fault Rare
If no mechanical or hydraulic cause can be identified, the printed circuit board may be misreading sensor data or failing to regulate the heating cycle correctly, causing the boiler to overheat. This is a less common but more costly possibility.
How to fix it
- Allow the boiler to cool down completely DIY safe
Do not attempt a reset immediately. Give the boiler at least 15–20 minutes to cool. Resetting a boiler that is still hot will not clear the root cause and may trip the fault again almost immediately.
- Bleed your radiators to release trapped air DIY safe
Using a radiator bleed key, open the bleed valve on each radiator (starting upstairs) until water flows steadily with no sputtering. Air pockets in the system can restrict circulation and contribute to overheating. Have a cloth ready to catch any drips.
- Check and top up system pressure if needed DIY safe
Look at the pressure gauge on the boiler front. It should read between 1.0 and 1.5 bar when the system is cold. If it is below 1.0 bar, use the filling loop — typically two interlinked valves beneath the boiler — to top up slowly to around 1.2 bar, then close the valves firmly.
- Reset the boiler DIY safe
On models with a REC10 controller, press the OK button to reset. On selector dial models, turn the dial to the Off/Reset position, wait a few seconds, then return it to your preferred heating mode. The manufacturer allows up to three reset attempts. If the E020 returns after one or two resets, stop — repeated resets without fixing the cause can mask a serious problem.
- Have a Gas Safe engineer inspect the circulation pump Gas Safe engineer
An engineer will test the pump for correct speed and pressure output. A seized or underperforming pump is the most likely culprit and will need to be replaced. This is not a DIY task — it involves draining down part of the system and working on sealed components.
- Arrange a system power flush if sludge is suspected Gas Safe engineer
If the pump tests fine, sludge or scale build-up inside the heat exchanger or pipework is the next most likely cause. A professional power flush forces high-velocity water and cleaning chemicals through the system to clear blockages. Fitting a magnetic filter afterwards will help prevent recurrence.
- Have the limit thermostat tested and replaced if faulty Gas Safe engineer
An engineer can check whether the thermostat itself is giving accurate readings or has failed prematurely. If it is triggering incorrectly, a replacement thermostat will be fitted. This is an internal boiler component requiring trained hands.
- Request a PCB diagnostic if no other cause is found Gas Safe engineer
If pump, sludge, air, and the thermostat have all been ruled out, the PCB may be at fault. An engineer can test the board's outputs and sensor readings. PCB replacement is one of the more expensive repairs, so get a written quote and weigh it against the age and condition of the boiler before proceeding.
Parts you may need
- Circulation pump (Grundfos or equivalent compatible) · from £85
- Limit thermostat / high-limit safety sensor · from £35
- Magnetic system filter (e.g. Adey Magnaclean Pro2) · from £65
- System inhibitor (central heating fluid treatment) · from £15
- PCB (Vokera-specific replacement board) · from £220
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£450, depending on the underlying cause.
Frequently asked questions
Can I just keep resetting the Vokera E020 and carry on using the boiler?
You can try one or two resets to see if the fault was a one-off event, but you should not keep resetting the boiler repeatedly. E020 is a safety shutdown triggered by overheating — if it keeps coming back, something is genuinely wrong with circulation or the thermostat, and continuing to override it risks damaging the heat exchanger or causing a more expensive failure. Call a Gas Safe engineer if the code returns after a reset.
How much does it typically cost to fix a Vokera E020 fault?
Most people with an E020 fault end up paying somewhere between £150 and £450 all in, depending on what the engineer finds. A pump replacement commonly falls in the £200–£350 range including labour, while a thermostat swap is usually at the lower end. A full system power flush typically adds £300–£500 on top of diagnosis. If the PCB turns out to be the cause, that can push costs higher — sometimes £400 or more for parts alone — which on an older boiler may make replacement worth considering.
What is the difference between Vokera fault codes E020 and A02?
Both codes relate to the limit thermostat, and Vokera documentation notes they share the same root cause — an overheating shutdown. The key practical difference is in how they are displayed and reset: E020 is typically shown on digital display models (such as the Evolve) and is described as a final fault requiring a manual reset, whereas A02 may appear on older or differently configured Vokera models. The diagnosis and repair steps are essentially the same for both.
Could low boiler pressure cause the Vokera E020 code?
Indirectly, yes. Low system pressure means there is less water circulating through the heat exchanger. With reduced water volume to absorb the burner's heat, temperatures can climb quickly and trip the limit thermostat. Checking and topping up pressure to around 1.2 bar is one of the first things to try, but if pressure keeps dropping, there is likely a leak or a faulty expansion vessel that a Gas Safe engineer will need to address.