Boiler
E13
The E13 error code on a Glow-worm boiler indicates a flow temperature sensor fault or an overheating condition — it’s a serious fault that will lock out your boiler until resolved. This is not a DIY repair; gas boiler work must be carried out by a Gas Safe registered engineer.
What does this error mean?
The E13 code means your Glow-worm boiler has detected an abnormally high flow temperature — the water leaving the heat exchanger is too hot, or the sensor measuring that temperature has failed. The boiler’s safety system shuts the unit down to prevent damage to internal components or, in worst cases, a dangerous overheat. Until the underlying fault is fixed, the boiler will not restart reliably.
Est. repair cost
£150–£350 for a Gas Safe engineer call-out, diagnosis, and parts (NTC sensor, pump, or power flush); new boiler replacement from £1,800–£2,500 installed
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Reset the boiler: Press and hold the reset button (usually marked with a flame or ‘R’) for 3–5 seconds. If the boiler fires up and runs normally, monitor it for 30 minutes. A one-off lockout can occur after a power cut or brief overheat.
Step 2 — Check your system pressure: Look at the pressure gauge on the boiler front panel. It should read between 1.0 and 1.5 bar when cold. If it’s below 0.8 bar, top up via the filling loop (refer to your Glow-worm manual for your specific model). Low pressure can restrict flow and trigger overheating.
Step 3 — Bleed your radiators: Air trapped in the system reduces circulation. Use a radiator bleed key to release air from the highest radiators in your home. Re-check boiler pressure afterwards and top up if it has dropped.
Step 4 — Check that all radiator valves are open: Closed thermostatic radiator valves (TRVs) or lockshield valves can restrict circuit flow and cause the boiler to overheat. Ensure at least two or three radiators in the home have fully open valves.
Step 5 — Do not attempt further repairs yourself: If the E13 returns after these basic checks, stop. The fault almost certainly requires a Gas Safe registered engineer. Attempting to open the boiler casing, replace components, or tamper with gas pipework is illegal without Gas Safe registration and potentially dangerous.
📞 When to call a professional
Call a Gas Safe registered engineer if the E13 error returns after a reset, or if the boiler is making unusual noises, emitting smells, or showing signs of leaking water. Tell the engineer: ‘My Glow-worm boiler is showing an E13 flow temperature fault and locking out after reset.’ This helps them bring the right parts — likely an NTC sensor, pump, or descaling kit — saving time and call-out cost.
⚖️ Repair or replace?
For a boiler under 10 years old, repair is almost always the right call — replacing a pump or NTC sensor typically costs £150–£350 all-in and restores full function. If your Glow-worm boiler is over 12–15 years old and has had previous faults, a new A-rated boiler (installed from around £1,800–£2,500) will be more cost-effective long-term, especially given rising energy costs. Get a like-for-like repair quote first, then compare it against a new boiler quote before deciding.