Ravenheat E31 Fault Code: Causes, Fixes & Repair Costs
What does the Ravenheat E31 fault code mean?
The E31 code on a Ravenheat boiler signals that the OpenTherm communication link between the boiler and its connected thermostat or controller has broken down. OpenTherm is a digital, two-way protocol that allows a compatible thermostat to continuously adjust the boiler's heat output in real time — rather than simply switching it on and off. When E31 appears, this dialogue has been interrupted, and the boiler cannot receive the commands it needs to operate correctly. The fault may be triggered by something as minor as flat thermostat batteries or a temporary signal dropout, but it can also point to wiring issues, a faulty thermostat receiver, or a problem with the boiler's PCB.
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
- Temporary communication dropout Common
A brief interruption to the OpenTherm signal — caused by electrical interference, a momentary power fluctuation, or a transient glitch in the thermostat — can be enough to trigger E31. The boiler locks out as a precaution, but a simple reset is often all that is needed to restore normal operation.
- Dead or low thermostat batteries Common
Battery-powered OpenTherm thermostats lose the ability to maintain their communication link when batteries run low. This is one of the most overlooked causes of E31 and one of the easiest to resolve. Batteries should ideally be replaced every six months as a matter of routine.
- Wiring fault between thermostat and boiler Sometimes
On wired OpenTherm installations, a loose terminal, a damaged cable, or a corroded connection can break the communication circuit. The fault may be intermittent at first, eventually causing a persistent E31 lockout.
- Faulty or incompatible thermostat or receiver Sometimes
OpenTherm is a standard with optional features, and not all devices from different manufacturers implement it identically. A faulty wireless receiver at the boiler, an incompatible controller, or a thermostat that has developed an internal fault can all prevent the required two-way exchange from taking place.
- Dust or debris inside the thermostat Rare
Accumulated dust on the internal contacts or circuitry of the thermostat can interfere with normal operation and disrupt the OpenTherm signal being sent to the boiler.
- Faulty boiler PCB Rare
If the OpenTherm communication circuitry on the boiler's printed circuit board has failed, the boiler will be unable to receive or interpret signals from the thermostat regardless of its condition. This is the least common cause but should be investigated if all other components check out.
How to fix it
- Reset the boiler DIY safe
Press the reset button (or cycle the boiler's on/off switch, depending on your model) to attempt to clear the fault. A temporary communication dropout will often resolve itself after a single reset. If the fault clears and does not return within a normal heating cycle, no further action is needed. Avoid resetting more than two or three times — repeated resets without resolution suggest an underlying fault that needs investigation.
- Check and replace the thermostat batteries DIY safe
If your OpenTherm thermostat runs on batteries, remove them and fit a fresh set. Even batteries that show a partial charge can struggle to maintain a stable communication signal. After fitting new batteries, allow the thermostat a minute or two to reconnect, then attempt a boiler reset.
- Check that the thermostat has power and is switched on DIY safe
Confirm the thermostat display is active and that it has not been accidentally switched off or lost its mains power supply (for hardwired models). Check any associated fuse spur is switched on and has not tripped.
- Gently clean the thermostat DIY safe
If your thermostat has an accessible interior (such as a removable cover), use a dry, soft brush or a can of compressed air to remove any visible dust from around the circuit board and terminals. Do not use water or spray cleaners. Reassemble, restore power, and retry the boiler reset.
- Inspect wiring connections between the thermostat and boiler Gas Safe engineer
A heating engineer should check the OpenTherm wiring terminals at both the thermostat and the boiler for loose connections, corrosion, or cable damage. The two OpenTherm wires carry both power and data, so even a partially loose terminal can cause intermittent faults. This work requires knowledge of the boiler's wiring diagram and should not be attempted by a homeowner.
- Test or replace the thermostat and receiver Gas Safe engineer
A heating engineer can use diagnostic equipment to determine whether the thermostat or its wireless receiver is generating a valid OpenTherm signal. If the device is found to be faulty or incompatible with your Ravenheat boiler, replacing it with a confirmed-compatible OpenTherm controller will resolve the E31 fault.
- Have the boiler PCB inspected and replaced if necessary Gas Safe engineer
If the wiring, thermostat, and receiver all test correctly, the fault is likely to lie within the boiler's PCB — specifically the OpenTherm communication circuitry. A Gas Safe registered engineer can test the PCB and advise whether repair or replacement is appropriate. On older Ravenheat boilers, the cost of a new PCB may make full boiler replacement a more sensible option.
- Call a Gas Safe registered engineer Gas Safe engineer
If the fault persists after you have tried the homeowner checks above, contact a Gas Safe registered engineer. They can carry out a full diagnostic of the OpenTherm system, wiring, thermostat, and boiler PCB, and carry out any necessary repairs safely and correctly.
Parts you may need
- OpenTherm-compatible thermostat (e.g. Honeywell, Nest, Drayton) · from £80
- Wireless OpenTherm receiver/module · from £45
- Ravenheat boiler PCB · from £220
- Thermostat wiring (per metre, low-voltage) · from £4
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 £60–£300, depending on the underlying cause.
Frequently asked questions
Can I fix the Ravenheat E31 fault myself?
Some of the most common causes are absolutely within a homeowner's reach — replacing flat batteries, cleaning the thermostat, and resetting the boiler cost nothing and take only a few minutes. However, if those steps do not clear the fault, you will need a heating engineer to investigate the wiring, thermostat receiver, or boiler PCB. Gas components and PCB work must always be handled by a Gas Safe registered professional.
Will the E31 fault come back after a reset?
If the original cause was a one-off communication glitch, a single reset is usually enough and the fault will not return. If E31 reappears after each heating cycle or within a few hours of resetting, there is an underlying fault — most likely with the wiring, the thermostat, or the boiler PCB — that needs a proper diagnosis rather than repeated resetting.
How much does it cost to fix the Ravenheat E31 fault?
Most people with an E31 fault pay somewhere between £60 and £300 all in. A straightforward thermostat replacement or wiring repair typically falls at the lower end of that range. If the boiler's PCB turns out to be the cause, parts and labour can push the bill towards £400 or more. On Ravenheat boilers that are over ten years old, a full boiler replacement is often better value than replacing a PCB, and a new condensing boiler will typically cut your heating bills as well.
Is OpenTherm the same as a standard on/off thermostat connection?
No — they are quite different. A conventional thermostat simply switches the boiler on when heat is needed and off when the set temperature is reached. An OpenTherm thermostat communicates digitally with the boiler, continuously adjusting the target flow temperature to match demand. This modulating control is more efficient but requires both devices to speak the same OpenTherm protocol. If you swap your thermostat for a non-OpenTherm model, the E31 fault will clear but you will lose the efficiency benefits of modulation.