Biasi E19 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi E19 fault code mean?
The E19 code appears on newer-generation Biasi boilers, including the Rinnova and Rinnova Adaptive ranges. It signals an 'Auxiliary Input Probe Anomaly' — meaning the boiler's control board has detected a problem with an additional temperature sensor (an NTC probe) connected to its auxiliary input. This probe feeds supplementary temperature data to the PCB; when the signal falls outside expected parameters, is absent, or is erratic, the boiler registers E19 and locks out as a safety measure. On the Rinnova Adaptive display this code appears as E19 + A. Note that older Biasi models (Riva Plus, Garda) use ER-prefixed fault codes rather than E-codes — if your boiler shows an ER code, this page does not apply.
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 or degraded auxiliary NTC probe Common
The auxiliary NTC temperature sensor itself has broken down or drifted so far out of its calibrated resistance range that the PCB can no longer interpret its signal. NTC probes wear over time, especially in systems with poor water quality or fluctuating temperatures, and a failed probe is the single most likely cause of E19.
- Loose, corroded, or broken probe wiring Common
A poor connection between the auxiliary probe and the PCB — caused by corrosion on terminals, a chafed cable, or a connector that has worked loose — can produce an intermittent or absent signal that the boiler interprets as a probe fault. This is particularly worth considering if the fault appears and disappears without a clear pattern.
- PCB misreading a good probe signal Sometimes
If the probe and its wiring both test within specification, the fault may lie with the PCB itself. The input circuit on the board can develop a fault that causes it to mis-read or reject an otherwise healthy sensor signal. PCB faults are less common than sensor or wiring issues but should be considered once other causes are ruled out.
- Incorrectly wired external or smart controls Sometimes
If a smart thermostat (such as a Nest, Hive, or Tado) has recently been fitted, incorrect wiring to the boiler's auxiliary input can cause the control board to detect a signal anomaly. E19 faults that appear shortly after a controls upgrade should prompt a check of the installation wiring.
How to fix it
- Reset the boiler once or twice DIY safe
Locate the reset button on the boiler's front panel, press and hold it for around 5–10 seconds until the display changes and the boiler attempts to restart. Allow up to 10 minutes for the ignition sequence to complete. If the boiler fires up and runs normally, monitor it over the next few hours. Do not attempt more than two or three resets in a row — if E19 returns each time, the underlying fault is still present and repeated resets will not fix it.
- Check whether any external controls were recently changed DIY safe
If a smart thermostat or other external control device was installed shortly before the fault appeared, this is worth noting before you call an engineer. You do not need to re-wire anything yourself — simply let the engineer know, as incorrect wiring to the auxiliary input is a straightforward thing for them to diagnose.
- Contact a Gas Safe registered engineer for diagnosis Gas Safe engineer
Because E19 points to an internal sensor, wiring, or PCB fault, professional diagnosis is required. An engineer will use a multimeter to check the resistance of the auxiliary NTC probe against its expected values at a given temperature, inspect the wiring loom and connectors for corrosion or damage, and test the PCB input circuit if the probe and wiring are found to be good. Do not attempt to test or disconnect probe wiring yourself — this involves live electrical components inside a gas appliance.
- Replace the faulty component as identified by the engineer Gas Safe engineer
In most cases the engineer will replace the auxiliary NTC probe, which is typically a straightforward part swap. If the wiring is at fault, terminals and cables will be repaired or replaced. Where the PCB is implicated, the engineer will advise on the cost of replacement versus the age and condition of the boiler — a PCB replacement on an older boiler can sometimes tip the balance towards a new boiler installation.
Parts you may need
- Auxiliary NTC temperature probe · from £35
- Probe wiring harness / connector · from £20
- Biasi Rinnova PCB (main control board) · from £220
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 £140–£320, depending on the underlying cause.
Frequently asked questions
Can I fix the Biasi E19 fault myself?
The initial reset is something any homeowner can safely do, but beyond that, E19 requires a Gas Safe registered engineer. The fault involves internal electrical components — specifically a temperature probe and its wiring — inside a gas appliance, and working on these without the correct qualifications is both illegal and potentially dangerous. A qualified engineer should carry out all testing and parts replacement.
How much does it cost to repair a Biasi E19 fault in the UK?
For the most common fix — replacing the auxiliary NTC probe — you can expect to pay roughly £140–£250 including parts and labour. If additional wiring work is needed, costs may rise to around £300–£320. If the PCB turns out to be the root cause, a board replacement can cost significantly more, often £350–£500 or above. As a general rule, if a repair quote is approaching £500 or more and the boiler is outside its warranty period, it is worth getting quotes for a new boiler installation to compare.
Is the Biasi E19 fault covered by warranty?
Biasi boilers come with a manufacturer's warranty of five to seven years depending on the model. If your boiler is within its warranty period, contact Biasi directly before arranging an independent engineer, as the repair or part replacement may be covered at no cost to you. Have your boiler's model number, serial number, and installation date to hand when you call.
How can I prevent the E19 fault from coming back?
Annual servicing by a Gas Safe engineer is the most effective way to catch probe and wiring deterioration before it causes a lockout. Keeping the system water clean (a magnetic filter helps trap sludge that can cause component stress), maintaining boiler pressure between 1 and 1.5 bar when cold, and ensuring any external controls are fitted by a qualified installer will all reduce the likelihood of sensor and electrical faults recurring.