Ravenheat CSI30 Fault Code: Causes, Fixes & Repair Costs
What does the Ravenheat CSI30 fault code mean?
Fault code 30 on the Ravenheat CSI 120 range reports a failed flue temperature reading — the sensor monitoring the exhaust gases has returned a reading the board cannot accept, or the flue temperature itself has moved outside the expected operating envelope. Ravenheat's terse guidance for this code is to check the operating system — in practice, that means verifying the flue temperature sensor and its circuit, and ruling out the genuine causes of abnormal flue temperatures: poor heat transfer through a scaled or sooted heat exchanger, and restricted flue flow. Because flue temperature is part of the boiler's safety monitoring, the unit stops rather than run blind.
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 flue temperature sensor Common
The thermistor in the flue path lives in the harshest environment in the boiler and is a known wear item. When it drifts, opens or shorts, the board loses its exhaust reading and raises code 30.
- Scaled or sooted heat exchanger raising flue temperature Sometimes
If heat is not transferring into the water properly, exhaust gases leave hotter than design. A genuinely high flue reading trips the protection. Usually picked up (and prevented) at annual service.
- Flue restriction Sometimes
A partially blocked or degraded flue changes exhaust behaviour and temperature at the sensor. Engineers inspect the flue run and terminal as part of diagnosing this code.
- Sensor wiring or board input fault Rare
As with any sensor circuit, the lead, connector or PCB input can fail and mimic a dead sensor. Ruled out by measurement at each point.
How to fix it
- Look at the flue terminal from outside DIY safe
Visually check the external flue terminal for obvious obstruction — leaves, nests, ice. Look only; never reach into or dismantle any part of the flue.
- Reset once DIY safe
A single reset distinguishes a transient reading from a hard fault. If code 30 returns during or soon after firing, leave the boiler off and book an engineer.
- Do not run the boiler repeatedly against this code DIY safe
Flue temperature monitoring is a safety function. If the temperature genuinely is abnormal, repeated running risks damage — treat recurrence as a stop signal.
- Engineer: test the sensor and inspect the combustion side Gas Safe engineer
A Gas Safe registered engineer will test the flue sensor and circuit, inspect the heat exchanger for scaling or sooting, check the flue run, and carry out a combustion analysis after any repair. All of this is sealed-system, combustion-side work.
Parts you may need
- Flue temperature sensor · from £35
- Heat exchanger cleaning kit/service 0
- Control PCB · from £170
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 £120–£320, depending on the underlying cause.
Frequently asked questions
What does fault 30 mean on a Ravenheat CSI 120?
The boiler has lost a valid flue temperature reading, or the exhaust temperature has gone outside its expected range. Most often the flue sensor itself has failed; less often the flue gases genuinely are too hot because of a scaled heat exchanger or a restricted flue. The boiler stops because this reading is part of its safety monitoring.
Can I clear code 30 and keep using the boiler?
One reset is reasonable. If the code returns, stop using the boiler and book a Gas Safe registered engineer — if the flue temperature really is abnormal, continuing to run risks damaging the heat exchanger, and the cause needs proper combustion-side investigation.
Would a service have prevented this?
Quite possibly, where the cause is a sooted or scaled heat exchanger — that builds gradually and is exactly what an annual service catches. Sensor failures, by contrast, are age-related and strike when they strike; the good news is the part is inexpensive.