Error E13

Safety first

- If you smell gas or detect symptoms of carbon monoxide (headaches, dizziness, nausea, flu‑like symptoms when heater is on), leave the property immediately, ventilate if safe to do so, call the gas emergency number and/or emergency services. Do not attempt any checks.

- Before any inspection switch the boiler off at the control panel and isolate the electrical supply at the mains. If you see water on or near electrical components keep the power off and do not touch internal parts.

Initial homeowner checks (safe to do without opening the boiler)

1) Record the fault: note the exact error code (E13), boiler model and serial number and take a clear photo of the display. This helps the engineer. 2) Attempt one reset only: follow your boiler manual (hold the reset button or turn the selector to R for ~5 seconds). If the fault clears and the boiler runs normally for a sustained period that may have been a transient event — but see below. Do not keep resetting more than once. 3) Check system pressure: look at the pressure gauge. Aim for the manufacturer's recommended range (typically around 1.0–1.5 bar for most domestic systems). If pressure is low and you know how to use the filling loop, you may top up to the correct pressure. If you are unsure, stop and call an engineer. 4) Bleed radiators: release air from radiators to restore circulation if some radiators are cool while others are hot. 5) Look for visible leaks, blocked external flue or condensate pipe (frozen condensate can cause other faults), and ensure the gas supply is on. 6) Listen for pump noises: if the pump is silent or making unusual noises while the boiler is trying to run, there may be a circulation fault.

If initial checks do not resolve the fault or E13 returns

- Do not continue to operate the boiler or repeatedly reset it. A persistent E13 likely means the thermal fuse has operated due to genuine overheating or there is internal damage. Continued attempts may worsen damage.

- Professional diagnostic checks an engineer will perform (do not attempt unless Gas Safe registered): verify the cause of overheating (pump operation, flow/return temperatures, blockages, scale or sludge in the heat exchanger), test system flow rate and pressure under operation, check for airlocks and stuck diverter valves, inspect condensate and flue paths, check wiring and continuity of the thermal fuse and related sensors, and inspect the heat exchanger for visible damage or corrosion.

- Possible outcomes: if the thermal fuse or wiring is faulty and the heat exchanger is undamaged, the engineer may be able to replace the fuse and repair wiring. If the heat exchanger has been damaged by overheating or severe scaling/corrosion, the heat exchanger will usually need replacement; in many cases for older boilers replacing the whole boiler is considered because the heat exchanger is an expensive part.

How to work with an engineer

- When you call for help, tell the engineer the exact error code (E13), the model and serial number, what initial checks you have already done (reset, pressure check, bled radiators, any recent work on the system) and whether there are any visible leaks or unusual noises. Provide the photo you took of the display if possible.

- Only a Gas Safe registered engineer should carry out internal repairs, replace the thermal fuse or the heat exchanger, or work on gas components.

Final points

- E13 is a serious fault and commonly requires professional attention. Do the safe homeowner checks above, but do not attempt internal repairs on the gas appliance. If the fault persists after the simple checks, book a Gas Safe engineer to diagnose and repair the boiler. If you suspect immediate danger (gas smell, CO symptoms, visible severe leaks) evacuate and call emergency services and the gas emergency number.