Wolf FC 27 Fault Code: Causes, Fixes & Repair Costs
What does the Wolf FC 27 fault code mean?
Error 27 on a Wolf boiler indicates a problem with one of the NTC (Negative Temperature Coefficient) temperature sensors. These thermistors monitor water temperature by varying their electrical resistance as the temperature changes, feeding live readings back to the boiler's PCB so it can control the burner safely. When the PCB detects a reading outside the expected range — or no signal at all — it raises Error 27 and locks the boiler out to prevent overheating or unsafe operation. Note on display codes: Wolf boilers display this fault as '27' or 'Error 27'. The letters 'FC' seen on some Wolf appliances relate to filter-cleaning reminders on Wolf cooker hoods and are unrelated to this boiler fault code.
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
- Failed or degraded NTC sensor Common
Over years of repeated heating and cooling cycles the sensor's internal resistance element can drift outside its specified range or fail entirely. This is the most common trigger for Error 27 on Wolf boilers and usually requires the sensor to be replaced with the correct Wolf-specification part.
- Damaged wiring or corroded connector Common
The cable, plug, or terminal block connecting the NTC sensor to the PCB can suffer from corrosion, heat damage, or a loose connection. Even a slightly poor contact can produce intermittent or out-of-range readings that mimic a dead sensor, causing repeated lockouts.
- Low system pressure causing misleading temperature readings Sometimes
If the system pressure has dropped significantly below the normal 1–1.5 bar operating range, reduced water flow can create localised hot spots that make the sensor produce abnormal readings. Always check the pressure gauge before assuming the sensor itself is at fault.
- PCB fault Rare
In rarer cases the fault lies not with the sensor but with the PCB input circuit that reads it. If a correctly specified replacement sensor still triggers Error 27, the PCB may need to be tested and potentially replaced — a more involved and costly repair, particularly for Wolf boilers where boards may need to be sourced from Germany.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on your Wolf boiler (usually a dedicated button on the control panel) and hold it for the duration specified in your user guide. A single reset can clear a temporary electronic glitch. If Error 27 returns promptly or the boiler locks out again within a short period, do not keep resetting — further investigation is needed.
- Check the system pressure gauge DIY safe
Look at the pressure gauge on the boiler front panel. A Wolf boiler typically operates correctly between 1.0 and 1.5 bar when cold. If the needle is below 1 bar, the system may be low on water. You can top it up via the filling loop — consult your user manual for the location and method. Stop filling once the gauge reaches around 1.2–1.3 bar and close the filling loop valves fully. If pressure keeps dropping, tell the engineer when you call.
- Check that the gas supply is working DIY safe
Confirm that other gas appliances in the property (cooker, gas fire) are working normally. If nothing is receiving gas, contact your gas supplier rather than an engineer. If gas is available elsewhere, the issue is boiler-specific and an engineer visit is needed.
- Have a Gas Safe engineer inspect the NTC sensor and wiring Gas Safe engineer
An engineer will access the boiler's internal components, use a multimeter to measure the sensor's resistance across different temperatures, and check the wiring harness and connector terminals for damage or corrosion. This requires removing the boiler casing, electrical isolation, and may involve partial draining of the water circuit — work that must only be carried out by a Gas Safe registered engineer.
- Sensor replacement if confirmed faulty Gas Safe engineer
If the NTC sensor is proven to be outside specification, the engineer will source and fit the correct Wolf-specification replacement. NTC sensors vary in their resistance characteristics, connector type, and temperature range — using a generic substitute not matched to your Wolf model can produce inaccurate readings or trigger further fault codes. Wolf-specific sensors may need to be ordered from Germany, which can add a few days to the repair timeline.
- PCB testing if the fault persists after sensor replacement Gas Safe engineer
Should Error 27 continue after a confirmed correct sensor has been fitted, the engineer should test the PCB sensor-input circuit. PCB replacement on Wolf boilers can be costly and the board may need to be sourced from Germany, so the engineer should confirm diagnosis carefully before ordering. At this stage it is also worth considering the overall age and condition of the boiler.
- Call a Gas Safe registered engineer Gas Safe engineer
If Error 27 has not cleared after checking pressure and performing a single reset, contact a Gas Safe registered engineer with experience of continental European boilers. Ask them to confirm Wolf boiler experience before booking, as parts sourcing and diagnostic familiarity can differ from common UK brands.
Parts you may need
- NTC temperature sensor (Wolf-specification) · from £35
- Sensor wiring harness / connector plug · from £20
- PCB (control board) · from £290
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 £150–£320, depending on the underlying cause.
Frequently asked questions
Can I fix Wolf Error 27 myself by replacing the sensor?
No. Although the sensor itself is an inexpensive part, accessing it requires removing the boiler casing, electrically isolating the appliance, and possibly draining part of the water circuit. This work must be carried out by a Gas Safe registered engineer. Fitting the wrong sensor — even one that looks identical — can cause inaccurate temperature readings or trigger additional fault codes.
Wolf parts are hard to find in the UK — how long will a repair take?
Generic components like pumps and expansion vessels can usually be sourced from UK heating suppliers quickly. However, Wolf-specific parts such as branded NTC sensors, control boards, and gas valves typically need to be ordered directly from Germany, which can add several days to the repair. Ask your engineer to check parts availability before booking so you can plan accordingly, especially in winter.
Could low boiler pressure be causing Error 27?
Possibly, though it is less common than a sensor or wiring fault. Significantly low pressure reduces water circulation and can cause localised temperature spikes that produce abnormal sensor readings. Check the pressure gauge — it should sit between 1.0 and 1.5 bar when the system is cold. Topping up via the filling loop is a safe DIY task. If the code remains after restoring pressure, the sensor or its wiring is the more likely culprit.
My Wolf boiler is older and keeps throwing faults — is it worth repairing?
If your boiler is over 12–15 years old and Error 27 is not the first fault you have dealt with, it is worth asking your engineer for an honest assessment of its overall condition. The relatively high cost of sourcing Wolf-specific parts from Germany, combined with the labour rates for multiple repairs, can make continued repair less economical than replacement — especially if the PCB is also involved, which can add £250–£400 or more on top of sensor costs.