Boiler
E198
The E198 error code on a Baxi boiler indicates a fault with the boiler’s internal temperature sensors or thermistor circuit, preventing the boiler from firing safely. It’s a lockout fault — your boiler will not run until the underlying issue is resolved.
What does this error mean?
Baxi uses the E198 code to signal that the boiler’s control board has detected an abnormal or implausible reading from one or more temperature sensors (thermistors) — typically the flow or return thermistor. The boiler locks out as a safety precaution because it cannot accurately monitor water temperature, which is essential for safe operation. Until the sensor gives a reliable reading, the boiler will remain in lockout and refuse to ignite.
Est. repair cost
£150–£300 for thermistor replacement; £300–£600 for PCB replacement (parts + Gas Safe labour)
🔍 Likely causes
🛠️ Step-by-step fix
Check the boiler pressure gauge — it should read between 1 and 1.5 bar when cold. If it’s below 1 bar, top up via the filling loop and attempt a reset.
Perform a manual reset: press and hold the reset button on the boiler fascia for 3–5 seconds (consult your Baxi manual for your specific model). If the boiler fires and runs normally, monitor it closely over the next 24 hours.
If the error returns after reset, do not attempt to open the boiler casing or touch the gas components — this is now a job for a Gas Safe registered engineer.
While waiting for an engineer, check that the boiler’s external wiring and thermostat connections are firmly plugged in and undamaged — this is safe to inspect visually without removing any panels.
Call a Gas Safe registered engineer and tell them the exact error code (E198) and which Baxi model you have. Mention how long the fault has been occurring and whether a reset temporarily resolved it — this helps them bring the right parts.
📞 When to call a professional
If the E198 error returns after a reset, or if the boiler will not reset at all, stop and call a Gas Safe registered engineer immediately — do not attempt to open the boiler casing or tamper with internal components. Tell the engineer you have a Baxi boiler showing E198, that you suspect a thermistor or PCB fault, and provide your boiler model number (found on the data plate inside the front panel). Gas boiler work beyond a basic reset is legally required to be carried out by a Gas Safe registered engineer in the UK.
⚖️ Repair or replace?
A thermistor replacement typically costs £150–£300 all-in for parts and labour from a Gas Safe engineer; a PCB replacement is more expensive at £300–£600 depending on the Baxi model. If your boiler is over 10–12 years old and the PCB has failed, replacement with a modern A-rated combi is likely more cost-effective long-term. For boilers under 8 years old in otherwise good condition, repair is almost always worth it.