Protherm F.13 Fault Code: Causes, Fixes & Repair Costs
What does the Protherm F.13 fault code mean?
The F.13 code appears on Protherm boilers when the control system detects a problem with the domestic hot water (DHW) tank temperature sensor. The boiler's electronics continuously monitor signals from all connected sensors, and when the signal from the DHW sensor is absent, out of range, or erratic, the boiler flags F.13 and may shut down to protect itself. On the Panther Condens series, engineers are directed specifically to check for a sensor short-circuit or a fault at the X16 connector. On the Gepard range, F.12 and F.13 are closely related codes both pointing to the DHW tank sensor circuit. The exact presentation can vary slightly between Protherm model families, so always cross-reference with your specific installation manual — but in most cases F.13 points firmly at the DHW sensor or its associated wiring and PCB connection.
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
- Faulty or failed DHW tank temperature sensor Common
The DHW temperature sensor itself has failed — either through age, overheating, or moisture ingress. When the sensor's resistance drifts outside acceptable limits or it stops producing a signal altogether, the control board raises F.13. This is the most frequent root cause and is confirmed by the boiler's diagnostic logic, which directs engineers to test the sensor first.
- Loose, damaged, or corroded wiring and connectors Common
The wiring loom or connector between the DHW sensor and the PCB — particularly the X16 connector on Panther models — can work loose over time due to vibration, or suffer damage from heat exposure and condensation. A poor connection produces an unreliable or open-circuit signal that the control board interprets as a sensor fault, even if the sensor itself is perfectly healthy.
- Faulty PCB (printed circuit board) Sometimes
If both the sensor and its wiring check out as sound, the control board may be misreading or failing to process the sensor signal correctly. PCB faults can stem from moisture ingress causing corrosion or short-circuits, dry solder joints that create intermittent failures, or general wear on an older board. This is typically only confirmed once the sensor and wiring have been ruled out.
How to fix it
- Reset the boiler once or twice DIY safe
Press and hold the reset button (usually marked with a flame or reset symbol — check your user manual if unsure) for the duration specified in your handbook. Wait two to three minutes to see if the boiler restarts without displaying F.13. A one-off nuisance fault can sometimes clear with a reset. If the code returns promptly after resetting, stop here and move to the next step — repeated resets will not resolve an underlying sensor or wiring fault.
- Do not attempt any internal component checks yourself Gas Safe engineer
Testing or replacing the DHW temperature sensor, inspecting the X16 connector, or examining the PCB all require the boiler casing to be opened and involve electrical components directly connected to a gas appliance. This work must only be carried out by a Gas Safe registered engineer. Attempting it without the correct qualifications is illegal and dangerous.
- Arrange a visit from a Gas Safe registered engineer for diagnosis Gas Safe engineer
A qualified engineer will follow the manufacturer's recommended diagnostic sequence: first testing the DHW sensor's resistance with a multimeter to confirm whether it is within specification, then inspecting the wiring loom and connectors (including X16 on Panther models) for damage, corrosion, or looseness, and finally assessing the PCB if the sensor and wiring are both healthy. This logical order prevents unnecessary part replacements.
- Have the faulty component replaced by the engineer Gas Safe engineer
If the sensor is found to be out of specification it will be replaced. If a wiring fault is identified, the engineer will repair or renew the affected section. If the PCB is implicated only after the other checks are clear, a replacement board will be fitted. On older Protherm boilers, the engineer may advise whether repair still represents good value compared with investing in a new appliance.
Parts you may need
- DHW tank temperature sensor (NTC) · from £25
- Wiring harness / connector repair kit · from £20
- Replacement PCB (control 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 £100–£350, depending on the underlying cause.
Frequently asked questions
Is the Protherm F.13 fault the same as F.12?
They are closely related. On the Gepard and Panther series, F.12 and F.13 both relate to the DHW tank temperature sensor circuit, with F.12 typically indicating an open-circuit (broken connection) and F.13 indicating a short-circuit condition at the sensor or its wiring. In practice, the diagnostic approach is the same — a Gas Safe engineer will test the sensor resistance and inspect the connector and wiring to determine exactly what has failed.
Can I still use my Protherm boiler for heating while F.13 is showing?
That depends on how your boiler responds to the fault. Some Protherm models will lock out entirely on F.13, while others may continue to provide central heating but suspend the DHW function. Even if the heating side appears to be working, you should arrange for an engineer to investigate promptly — running a boiler with an active sensor fault can mask developing problems and may cause further damage.
How much does it cost to fix a Protherm F.13 fault in the UK?
For the majority of F.13 faults — a sensor swap or a wiring repair — you can expect to pay roughly £100–£350 including call-out, parts, labour, and VAT. A straightforward sensor replacement typically sits at the lower end of that range. If the PCB turns out to be the culprit, the total cost can rise to £400–£550 given the higher cost of the board itself, but a PCB fault is the least common outcome and is only confirmed after the sensor and wiring have been checked first.
Why does my Protherm keep showing F.13 even after I reset it?
A persistent F.13 that returns immediately or within a short time after resetting almost always indicates a genuine hardware fault — a failing sensor, a damaged connector, or a PCB issue — rather than a temporary glitch. Resetting the boiler more than two or three times without addressing the underlying cause is not recommended. You should book a Gas Safe registered engineer to carry out a proper diagnosis so the faulty component can be identified and replaced.