Error F.13

Safety precautions:

- If you smell gas, turn off the gas supply, turn off the boiler at the mains, leave the building and call your gas emergency number immediately. Do not attempt repairs.

- Switch the boiler off at the mains before touching any internal covers. Do not remove sealed panels or work inside the boiler unless you are a qualified engineer.

- Allow the boiler to cool before touching pipes or components to avoid scalding.

Initial checks a homeowner can do:

1) Note the exact fault code and any accompanying messages. Try a simple reset following the boiler’s manual (usually switch off, wait 30 seconds, switch on and press the reset button). If the fault returns immediately, proceed with checks below.

2) Check the system pressure on the boiler pressure gauge. Normal cold operating pressure is typically around 1.0–1.5 bar (check your manual). If pressure is significantly below 1 bar or shows zero, low water is likely.

3) Look for visible leaks under/around the boiler, pipework or radiators. Also check the condensate pipe (usually a plastic pipe to a drain or outside) for damage, disintegration or outlet blockage.

4) Listen for the pump when the boiler calls for heat: a working pump will make a quiet low-level noise; a seized pump may be silent or noisy. Do not touch moving parts.

Specific actions to try (homeowner-level):

5) If pressure is low, repressurise the system using the filling loop according to the boiler handbook: isolate the boiler electrically, open the filling loop valves slowly while watching the pressure gauge, bring it to the recommended pressure (usually ~1.0–1.5 bar) then close the valves and bleed a radiator to remove trapped air. If you are unsure how to use your filling loop consult the manual or contact an engineer.

6) After repressurising, switch the boiler back on and reset the fault. Observe whether the boiler runs normally and whether the F.13 clears.

7) If condensate pipe freezing could be suspected (outdoor pipe in cold weather), thaw safely with warm water/cloth. If condensate trap or pipe is blocked or disintegrated and you can see this externally, clear or replace the external plastic pipe if confident; otherwise call a pro. Be cautious—do not force internal components.

8) Bleed radiators to remove air if symptoms suggest airlock; then re-check pressure and operation.

When to call a professional:

- If the fault persists after correct system pressure and basic checks, or if you cannot find the source of a leak or block, stop further DIY. F.13 can also be caused by internal blockages, a failed pump, damaged sensors (NTCs) or water-damaged electronics/thermistors inside the boiler — these require diagnostic tools and expertise.

- If you find water damage inside the boiler casing, disintegrated condensate parts, or electrical/ sensor faults, isolate the boiler and book a qualified heating engineer (Gas Safe registered or equivalent) to inspect and repair.

What the engineer may do (for your information):

- Check wiring and sensor resistances (NTC sensors), verify flow/return temperatures, and read diagnostic logs.

- Inspect and test the pump for seizure or low flow and replace if necessary.

- Replace defective sensors (flow/return/cylinder NTC), repair wiring, replace condensate trap or pipework, and clear internal blockages. Repair/replace parts only by a qualified installer.

Final notes:

- Do not attempt electrical repairs, sensor replacements, or internal dismantling unless you are a trained and certified engineer. Incorrect repairs can create safety risks.

- If you have tried safe repressurisation and basic checks and the boiler still shows F.13, contact a qualified heating engineer to prevent further damage.