Boiler
E20
The E20 error code on a Glow-worm boiler indicates a fault with the central heating pump or water circulation — it’s a moderately serious fault that will lock out your boiler and leave you without heating or hot water until it’s resolved.
What does this error mean?
The E20 code tells you that your boiler’s internal controls have detected a problem with water circulation through the heating circuit. This usually means the pump isn’t moving water around the system at the correct flow rate, or the pump has seized or failed entirely. Left unresolved, this can cause the heat exchanger to overheat and sustain permanent damage.
Est. repair cost
£150–£350 for pump replacement by a Gas Safe engineer; PCB repair or replacement £200–£450
🔍 Likely causes
🛠️ Step-by-step fix
Check the boiler pressure gauge — it should read between 1 and 1.5 bar when cold. If it’s below 1 bar, repressurise the system using the filling loop (consult your Glow-worm manual for your specific model). Then reset the boiler by pressing and holding the reset button for 3–5 seconds.
Check all lockshield and isolating valves on radiators and pipework are fully open — a partially closed valve can restrict circulation enough to trigger E20.
Bleed your radiators to release any trapped air, starting with the radiator furthest from the boiler. Low gurgling sounds or slow heat-up times suggest an airlock.
After completing steps 1–3, attempt a boiler reset. If the boiler fires up and runs without returning the E20 code within 10–15 minutes, the fault may have been pressure or air-related.
If the E20 returns immediately or the boiler won’t reset, do not attempt further DIY. The pump itself or the PCB is likely at fault — this requires a Gas Safe registered engineer.
📞 When to call a professional
Call a Gas Safe registered engineer if the E20 error returns after a reset, if you can hear the pump humming but the heating isn’t warming up (seized pump), or if you’re unsure about any step above. Tell the engineer you have an E20 fault code and describe any symptoms — unusual noises, cold radiators, or pressure fluctuations — so they can bring the right parts.
⚖️ Repair or replace?
A pump replacement on a Glow-worm boiler typically costs £150–£350 all-in with a Gas Safe engineer, depending on the pump model and labour rates in your area. If your boiler is over 10–12 years old and this isn’t the first fault, it’s worth getting a replacement quote — a new A-rated combi boiler costs £1,800–£3,000 installed but will be far more efficient. For a boiler under 8 years old with no prior history of faults, repair is almost always the right call.