Ravenheat F86 Fault Code: Causes, Fixes & Repair Costs
What does the Ravenheat F86 fault code mean?
The F86 code on a Ravenheat boiler signals that the PCB has detected a problem with the electrical contact or signal from a connected underfloor heating (UFH) system. In plain terms, the boiler is not receiving the expected electrical handshake from the UFH circuit — this could be an open contact, a disconnected connector, or a wiring fault somewhere between the boiler's UFH input terminals and the underfloor heating controls. The boiler may lock out or simply refuse to respond to UFH heat demands until the issue is resolved.
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
- Broken, loose, or damaged wiring between boiler and UFH wiring centre Common
The most common root cause. The cable running from the boiler's UFH input terminals to the underfloor heating wiring centre or manifold wiring board can develop loose connections, corrosion at terminations, or outright breaks — particularly if the wiring has been disturbed during other work or has aged. A broken circuit here will cause the PCB to flag the contact as open.
- Faulty UFH wiring centre or relay Common
The wiring centre distributes signals to individual zone actuators. If the relay inside the wiring board fails, or the board itself develops a fault, the boiler will no longer receive a valid UFH demand signal. The boiler then registers the contact as absent and logs F86.
- Defective zone actuator on the manifold Sometimes
Each UFH zone is controlled by a motorised actuator that opens and closes when the thermostat calls for heat. A failed actuator — or one whose end-switch has stopped sending a feedback signal — can disrupt the contact circuit, triggering this fault code.
- No mains power to the UFH wiring boards Sometimes
If the dedicated isolator switch supplying the UFH wiring centre has tripped or been inadvertently turned off, the entire UFH control circuit loses power. The boiler sees no signal on its UFH input and raises F86. This is a surprisingly easy-to-miss cause.
- PCB fault on the boiler Rare
In a minority of cases the boiler's own PCB develops a fault on the UFH input circuit — either the input terminals or the onboard logic that reads the UFH contact signal. If all external wiring and UFH components check out correctly, the PCB itself may be at fault.
How to fix it
- Reset the boiler DIY safe
Press and hold the boiler's reset button (or toggle the on/off switch as described in your Ravenheat user manual) to clear the fault. If F86 disappears and does not return, monitor the system over the next few heating cycles. If it comes straight back, a reset alone will not cure the underlying issue and you should continue to the next steps.
- Check the UFH isolator switch and mains power supply DIY safe
Locate the dedicated isolator switch for your underfloor heating wiring centre — typically on or near the consumer unit or close to the manifold cupboard. Confirm it is in the ON position. If it has tripped, switch it back on and see whether the system resumes normally. If it trips repeatedly, do not keep resetting it — there is an electrical fault that needs a qualified electrician or Gas Safe engineer to investigate.
- Check the room thermostat or UFH zone controller DIY safe
Inspect the UFH thermostat for any displayed error messages and replace batteries if low — a thermostat that has lost power will stop sending a demand signal. Reset the thermostat according to its own manual and check whether a heat demand is now being registered. If the thermostat appears to be working correctly but F86 persists, the fault lies elsewhere in the circuit.
- Have a qualified engineer test wiring continuity and connections Gas Safe engineer
A Gas Safe registered engineer (or qualified electrician working alongside one) should carry out a continuity test on the wiring between the boiler's UFH input terminals and the wiring centre. Loose terminations, corroded connectors, and cable damage will show up at this stage. Many F86 faults are resolved simply by remaking connections or replacing a short section of cable.
- Have the UFH wiring centre and relays inspected and replaced if faulty Gas Safe engineer
If the wiring checks out, the engineer should test the wiring centre's relay and board for correct operation. A defective relay or wiring board will need to be replaced; this is straightforward work for an experienced heating engineer and is typically the most common repair outcome for F86.
- Have the manifold actuators checked Gas Safe engineer
The engineer should confirm that each zone actuator opens and closes correctly and that end-switch feedback is reaching the wiring centre. A stuck or failed actuator should be replaced; these are relatively inexpensive components and the work is not complex for a competent engineer.
- Have the boiler PCB inspected if all external components are sound Gas Safe engineer
If the wiring, wiring centre, and actuators all test correctly, the PCB's UFH input circuit may be at fault. PCB diagnosis and replacement must be carried out by a Gas Safe registered engineer. Given the cost of a PCB, the engineer should confirm this diagnosis with confidence before ordering the part — particularly on older Ravenheat boilers where replacement value versus boiler age should be considered.
Parts you may need
- UFH wiring centre / wiring board · from £55
- Zone actuator (motorised valve head) · from £25
- Boiler PCB (Ravenheat) · from £220
- Wiring centre relay (replacement relay module) · from £15
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–£320, depending on the underlying cause.
Frequently asked questions
Can I fix a Ravenheat F86 fault myself?
Some initial checks are within a homeowner's ability — confirming the UFH isolator hasn't tripped, replacing thermostat batteries, and resetting the boiler. However, the underlying cause of F86 is almost always an electrical wiring or component fault that requires proper testing with a multimeter and, in many cases, replacement of a component. This work should be carried out by a Gas Safe registered engineer or a qualified electrician working with one. Attempting to probe or reconnect wiring at the boiler terminals yourself risks both injury and voiding your warranty.
How much does it cost to repair a Ravenheat F86 fault in the UK?
For the majority of F86 repairs — typically a wiring fault, a failed relay, or a defective wiring centre — you should budget between roughly £100 and £320 including parts and labour. A simple loose connection found and remade during a single visit sits at the lower end; replacing a wiring board or actuators sits in the middle. A PCB replacement is less common but can push costs to £400 or more; on a Ravenheat boiler that is over ten years old, it is worth getting a new-boiler quote at that point for comparison.
Will the boiler still provide hot water and radiator heating with an F86 fault?
It depends on how the system is wired and how the boiler responds to the fault. In some configurations the boiler will continue to serve radiators and domestic hot water but simply refuse to fire in response to UFH demands. In others, the F86 fault causes a full lockout. Either way the fault needs to be resolved promptly to ensure reliable heating throughout the property.
What is the UFH contact the F86 code refers to?
Ravenheat boilers with underfloor heating compatibility have dedicated input terminals on their PCB that expect an electrical signal when the UFH system is calling for heat. This contact is usually provided via a relay or switched live from the UFH wiring centre. F86 is raised when the PCB detects that this contact is open, absent, or behaving unexpectedly — essentially meaning the boiler cannot confirm whether a legitimate UFH demand is present or not.