Ravenheat E04 Fault Code: Causes, Fixes & Repair Costs
What does the Ravenheat E04 fault code mean?
The E04 code on a Ravenheat boiler indicates that the PCB has detected a problem with the domestic hot water (DHW) NTC thermistor — the small temperature-sensing probe responsible for monitoring the temperature of your hot water. When this sensor sends a signal that falls outside the expected range, or stops responding altogether, the boiler logs E04 and shuts down to protect the system. This means your hot water is likely to stop working, though central heating may or may not be affected depending on the model. Note: Ravenheat Manufacturing Limited was dissolved in 2025, so parts availability is becoming increasingly limited — worth bearing in mind before committing to a repair.
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 degraded NTC thermistor Common
The DHW NTC thermistor is a small, relatively fragile component. Over time the probe can corrode, crack, or simply fail electrically, causing it to report temperature readings that are out of range or stuck at an implausible value. This is the single most common trigger for E04.
- Damaged or loose wiring to the sensor Common
The two-wire connection between the DHW sensor and the PCB can develop faults — loose terminals at either end, chafed insulation, or corrosion on the connector pins. Any of these can break or distort the signal reaching the PCB, mimicking a dead sensor even when the sensor itself is fine.
- Limescale build-up around the sensor Sometimes
In hard-water areas, scale deposits can accumulate around the sensor probe. The scaled-up area heats unevenly, causing the thermistor to read a higher temperature than the actual bulk water temperature. The boiler interprets this as an overtemperature or erratic sensor condition and shuts down.
- PCB unable to read the sensor signal Rare
If the PCB input circuit for the DHW sensor develops a fault, it may report E04 even when the sensor and wiring are both healthy. This is worth investigating only after the sensor and wiring have been confirmed to be sound, as PCB repairs or replacements are significantly more expensive.
How to fix it
- Check your gas supply is working DIY safe
Before anything else, confirm that other gas appliances in your home (e.g. a gas hob) are working normally. If there is no gas supply to the property, contact your gas supplier rather than investigating the boiler further.
- Reset the boiler once or twice DIY safe
Press and hold the on/off or reset button as described in your Ravenheat user guide. If the fault clears and the boiler runs normally for a while before E04 returns, this points to an intermittent sensor or wiring fault rather than a total failure. Do not reset more than two or three times in quick succession.
- Check system pressure DIY safe
Low system pressure can sometimes contribute to erratic sensor readings. Check the pressure gauge on the boiler — it should read between 1 and 1.5 bar when cold. If it has dropped below 1 bar, top it up via the filling loop and reset. If pressure keeps dropping, mention this to your engineer as it suggests a separate leak or expansion vessel issue.
- A Gas Safe engineer should inspect the sensor wiring Gas Safe engineer
An engineer will check the wiring harness from the DHW thermistor to the PCB — looking for corrosion at the terminals, loose push-fit connectors, or damaged insulation. This step is quick and often resolves E04 without any parts being needed.
- A Gas Safe engineer should test and replace the DHW NTC thermistor Gas Safe engineer
Using a multimeter, the engineer will measure the thermistor's resistance at a known water temperature and compare it against the expected value. A reading that is open-circuit, short-circuit, or significantly off-spec confirms the sensor has failed. Compatible replacement sensors (e.g. Ravenheat part TS.128, suitable for RSF, CSI, and LS series) are inexpensive — typically a few pounds — but given Ravenheat's dissolution in 2025, the engineer should confirm parts availability before attending.
- If the sensor and wiring are both sound, the PCB should be investigated Gas Safe engineer
A Gas Safe engineer with boiler electronics experience can check the PCB's sensor input circuit. Given the increasing scarcity of Ravenheat PCBs following the company's closure, the engineer may advise that a PCB replacement is uneconomical on an older boiler.
- Consider whether boiler replacement is the better option DIY safe
If your Ravenheat boiler is more than 10 years old and the engineer identifies a PCB fault or other major component failure, replacement parts may be unavailable or prohibitively expensive. Discuss with your engineer whether a like-for-like boiler replacement from a currently trading manufacturer offers better long-term value.
Parts you may need
- Ravenheat DHW NTC thermistor (e.g. part TS.128, RSF/CSI/LS compatible) · from £12
- Sensor wiring harness / connector (if damaged) · from £18
- Ravenheat PCB (if sensor input circuit failed — check availability) · from £120
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–£220, depending on the underlying cause.
Frequently asked questions
Can I fix the Ravenheat E04 fault myself?
The only homeowner-safe steps are checking your gas supply is on, topping up the system pressure if it has dropped, and resetting the boiler once or twice. The actual diagnosis and repair — testing the thermistor with a multimeter, replacing it, or investigating the PCB — must be carried out by a Gas Safe registered engineer. Working on internal boiler components without Gas Safe registration is illegal and potentially dangerous.
How much does it cost to fix a Ravenheat E04 fault in the UK?
If the fault is simply a failed DHW thermistor, you are typically looking at £100–£220 all-in, covering a Gas Safe engineer's call-out, a short labour time, and the sensor part (which itself costs only a few pounds). If the wiring harness also needs replacing the cost is similar. A PCB replacement would cost more — potentially £250–£400 including labour — but given Ravenheat's closure in 2025, finding a genuine PCB is increasingly difficult and expensive.
Ravenheat has gone out of business — can I still get parts for an E04 repair?
Ravenheat Manufacturing Limited was dissolved in 2025. Basic consumable parts like NTC thermistors are generic enough that compatible sensors remain available from independent boiler parts suppliers. However, proprietary components such as PCBs, gas valves, and heat exchangers are becoming scarce. If your engineer identifies a major component fault alongside the sensor issue, it is worth getting a boiler replacement quote at the same time, as repair costs may approach or exceed the price of a new boiler from a currently trading brand.
Will the Ravenheat E04 fault affect my central heating as well as hot water?
E04 specifically relates to the domestic hot water temperature sensor, so central heating operation may continue normally on some Ravenheat models. However, on models where the DHW fault triggers a full lockout, both heating and hot water will be unavailable until the fault is cleared. Either way, the boiler should not be left running indefinitely in a fault state — arrange for an engineer to investigate promptly.