Biasi E99 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi E99 fault code mean?
The E99 fault code on Biasi boilers indicates that the PCB (printed circuit board) — the electronic control unit that governs every function of the boiler — is reporting that it is not configured or has lost its programmed settings. In practical terms, the boiler's 'brain' either does not recognise a valid configuration, has had its settings wiped (for example after a power disruption or board replacement), or the board itself has developed a hardware fault. Until the PCB is correctly configured or replaced, the boiler will not operate. This fault appears across several Biasi models including the Rinnova combi and Rinnova system boiler ranges. Because the fix involves accessing internal electronics and, in most cases, entering a protected engineer parameter mode, this is strictly an engineer-only fault — it is not resolvable by a homeowner.
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
- Newly fitted or replacement PCB not yet configured Common
When a PCB is replaced, the new board arrives in a blank or default state and must be programmed to match the specific boiler model and its parameters. If an engineer fitted a replacement board without completing the configuration procedure — which involves holding two specific keys simultaneously for five seconds until 'HiS' appears on the display and then stepping through the settings — the boiler will immediately display E99. This is the single most common reason for this code appearing.
- PCB configuration lost after a power surge or interruption Sometimes
A significant power cut, voltage spike, or sustained distortion of the mains supply waveform can corrupt the stored settings on the PCB's memory. The board remains physically intact but behaves as though it has never been set up. Biasi's own service documentation for the related E89 internal error code explicitly references mains supply waveform distortion as a cause of electronic faults, and the same mechanism can produce an E99 condition.
- PCB hardware failure Sometimes
If the control board has developed a genuine fault — whether through age, overheating, component failure, or damage — it may report itself as unconfigured even if it was previously working correctly. Unlike a simple reconfiguration, a hardware failure means the board must be replaced and then programmed before the boiler will run again.
- Water ingress or internal leak near the PCB Sometimes
A dripping heat exchanger, leaking pump seal, or weeping joint inside the boiler casing can allow moisture to reach the PCB. Water damage can corrupt stored memory, cause short circuits across control pins, or degrade the board to the point where it can no longer retain its configuration. Always check for signs of water damage or staining around the PCB if E99 appears without an obvious cause.
- Loose or damaged wiring to the control board Rare
Poor connections on the wiring loom, a dislodged connector, or chafed cable insulation can cause intermittent signals to the PCB. In some cases this can cause the board to behave erratically and trigger a configuration error. A thorough wiring inspection should always be carried out before replacing the board.
How to fix it
- Check that your gas supply is working DIY safe
Before assuming the boiler electronics are at fault, confirm that other gas appliances in your home (hob, fire) are working normally. If there is no gas supply, contact your gas network operator. This step rules out a simple supply interruption that could have caused the boiler to lose power unexpectedly.
- Check the boiler's system pressure DIY safe
Look at the pressure gauge on the boiler — it should sit between 1.0 and 1.5 bar when cold. If it reads below 0.8 bar, top up via the filling loop following your boiler's user guide. Low pressure alone will not cause E99, but it is good practice to ensure the system is in the correct state before an engineer visits.
- Attempt a single boiler reset DIY safe
Press and hold the reset button on the boiler's control panel as described in your user guide. Wait for the boiler to restart and monitor it for 10–15 minutes. If E99 clears and does not return, keep an eye on it over the next day or two. If the code comes back, do not keep resetting — repeated resets will not fix an underlying electronic fault and may mask important diagnostic information for the engineer.
- Check for any obvious signs of a water leak inside the boiler casing DIY safe
With the boiler off and cooled down, remove the front casing panel if you are comfortable doing so (this does not involve gas or electrical work — simply unclipping or unscrewing the cover). Look for water staining, corrosion, or damp patches near the PCB, which is typically a green or grey circuit board mounted near the top or front of the appliance. If you see evidence of a leak, note where it appears to be coming from and report this to the engineer — do not attempt to repair it yourself.
- Contact a Gas Safe registered engineer to diagnose and resolve the fault Gas Safe engineer
Resolving E99 requires an engineer to access the boiler's protected parameter setting mode (a key-hold sequence that brings up the 'HiS' menu on the display) and work through the configuration procedure. If reconfiguration does not resolve the fault, the engineer will test the PCB and associated wiring before deciding whether a board replacement is needed. Always ask your engineer to verify there is no underlying cause — such as a wiring fault, water ingress, or failing sensor — before fitting a new PCB, as replacing the board without addressing the root cause may result in the same fault recurring. If your Biasi boiler is within its warranty period (typically five to seven years depending on model), contact Biasi UK directly before authorising any paid repair.
Parts you may need
- Biasi PCB (control board) — model-specific · from £220
- PCB wiring loom / connector set · from £35
- Pump seal kit (if water ingress suspected) · from £18
- Heat exchanger O-ring / seal set (leak prevention) · from £22
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–£400, depending on the underlying cause.
Frequently asked questions
Can I fix Biasi E99 myself by resetting the boiler?
A reset is unlikely to clear E99 permanently because the code indicates the PCB has lost its configuration or has failed — neither of which a reset can address. You can try one reset to see if the fault clears temporarily, but if E99 returns you will need a Gas Safe registered engineer. Do not reset the boiler repeatedly, as this does not constitute a repair and can delay a proper diagnosis.
How much does it cost to fix a Biasi E99 fault in the UK?
If the PCB simply needs re-programming (no parts required), most engineers will charge their standard call-out and labour rate, typically £120–£180 all in. If the PCB needs to be replaced, you are looking at roughly £200–£400 including parts and labour for most Biasi models, though prices in London and the South East tend to sit at the higher end. In rare cases where a board is difficult to source or the boiler is an older model, costs can exceed this — if a quote comes in above £450 or so, it is worth comparing it against the cost of a new boiler, particularly if the appliance is more than eight to ten years old.
Why has E99 appeared after my boiler's PCB was just replaced?
This is actually the most common scenario for E99. A replacement PCB is supplied in an unconfigured state and must be programmed to the specific boiler model before it will operate. The configuration process involves entering a protected engineer menu (triggered by holding two control keys for five seconds until 'HiS' shows on the display) and stepping through the required parameters. If the engineer who fitted the board did not complete this procedure, or if the programming was interrupted, E99 will show. Contact the engineer who carried out the replacement — this should be resolved under their workmanship warranty at no additional cost to you.
Is it worth repairing a Biasi boiler showing E99, or should I replace it?
If your Biasi boiler is relatively new (under seven years old) and in otherwise good condition, a PCB reconfiguration or replacement is usually worthwhile and can restore many more years of reliable service. If the boiler is older, has a history of faults, or the repair quote is approaching or exceeding half the cost of a new boiler installation (typically £2,000–£3,500 for a new combi), replacement often makes more financial sense. Also remember that Biasi boilers carry a manufacturer's warranty of five to seven years depending on the model — if yours is still in warranty, contact Biasi UK before agreeing to any paid repair.