Biasi E118 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi E118 fault code mean?
The E118 fault code appears on newer Biasi boiler models — including the Inovia and Advance Plus — and signals that the system water pressure has fallen critically low, typically below 0.5 bar. At this point the boiler's safety controls kick in and shut the unit down entirely, so you'll lose both heating and hot water until the pressure is restored and the fault is cleared. On older Biasi ranges such as the Riva Plus and Garda you may see an equivalent ER-series code instead, but the underlying issue and the steps to resolve it are identical. A sealed central heating system relies on a specific pressure range to circulate water properly; when that pressure collapses, the boiler simply cannot do its job safely.
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
- Gradual system leak Common
Small weeps at radiator valves, pipe joints, or towel-rail fittings are the most frequent reason pressure slowly drops over days or weeks. The leak may not leave an obvious puddle — damp patches behind walls or under floorboards, or slight corrosion around valve bodies, are common clues. If pressure keeps falling after you repressurise, a leak is the likely culprit.
- Pressure lost after bleeding radiators Common
Releasing trapped air from radiators is good practice, but every bleed key turn also lets a small amount of water escape. If the system is not topped back up to 1.0–1.5 bar afterwards, pressure can drop far enough over the following hours to trigger E118.
- Faulty or weeping pressure relief valve (PRV) Sometimes
The PRV is a safety device designed to release water if the system ever over-pressurises. When it starts to fail it can dribble water away continuously even at normal pressures, causing a slow but persistent pressure drop. You'll often spot this as a drip from the discharge pipe outside the property.
- Waterlogged or failed expansion vessel Sometimes
The expansion vessel absorbs the rise in water volume as the system heats up. Over time the internal diaphragm can rupture or lose its pre-charge, causing pressure to swing erratically. A failed vessel can make the PRV open unnecessarily, which accelerates pressure loss.
- Microscopic leaks in pipework or heat exchanger Rare
Pinhole corrosion — particularly in older steel pipework or aluminium heat exchangers — can cause pressure to fall so slowly it's barely noticeable week to week. These leaks are often invisible to the naked eye and may need specialist leak detection equipment to locate.
How to fix it
- Check the pressure gauge reading DIY safe
Look at the gauge on the boiler's front panel (or beneath the casing on some models). A healthy cold system sits between 1.0 and 1.5 bar. A reading below 0.8–1.0 bar confirms low pressure is behind the E118 fault and that repressurising is needed before anything else.
- Locate the filling loop DIY safe
The filling loop is usually a short flexible braided hose with a valve at each end, found beneath the boiler. Some Biasi models have an internal filling device accessed via a small tap or lever on the underside of the appliance. Consult your user manual if you are unsure — the loop should be clearly labelled.
- Repressurise the system to 1.5 bar DIY safe
With the boiler off and cooled down, slowly open both filling-loop valves (or the single internal tap) and watch the gauge rise. When it reaches 1.5 bar, close both valves firmly. Do not exceed 2.0 bar. If the gauge refuses to move or you cannot locate the filling loop, stop and call an engineer rather than guessing.
- Reset the boiler DIY safe
Once pressure is restored, press and hold the reset button on the control panel for a few seconds as described in your Biasi user manual. The boiler should restart and the E118 code should clear. If it restarts and runs normally, you're done for now — but continue monitoring.
- Monitor pressure daily for at least one week DIY safe
Check the gauge at the same time each day. A one-off drop that stabilises after repressurising is usually nothing to worry about. If pressure falls again within 24–48 hours, stop repressurising — repeated topping-up masks an ongoing leak and can accelerate corrosion. Move on to the next step.
- Inspect visible pipework, radiator valves, and the PRV discharge pipe DIY safe
Walk around your home checking exposed pipes, radiator valve bodies, and the area beneath the boiler for damp patches, rust staining, or drips. Go outside and check whether the boiler's discharge (doom) pipe is dripping — a weeping PRV will show itself here. Photograph anything suspicious before calling an engineer.
- Call a Gas Safe registered engineer to locate and repair any leak or faulty component Gas Safe engineer
If pressure keeps dropping, or if you spot any damp, drips, or a continuously weeping PRV, a Gas Safe engineer needs to pressure-test the system, carry out a leak-detection survey if required, and replace any faulty components such as the PRV, expansion vessel, or damaged pipework. Do not continue repressurising as a workaround — the underlying fault will worsen.
Parts you may need
- Expansion vessel (replacement) · from £55
- Expansion vessel pre-charge valve / Schrader valve · from £8
- Pressure relief valve (PRV) · from £25
- Filling loop assembly · from £18
- Pressure gauge · from £20
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 £90–£320, depending on the underlying cause.
Frequently asked questions
Can I fix the Biasi E118 fault myself without calling an engineer?
In many cases, yes — if the only problem is that the system pressure has dropped, repressurising via the filling loop and resetting the boiler is a perfectly safe DIY job that costs nothing. However, if pressure keeps falling after you top it up, that points to a leak or a faulty component such as the pressure relief valve or expansion vessel, which do require a Gas Safe registered engineer to diagnose and repair.
How often should my Biasi boiler lose pressure?
A well-maintained sealed system should hold its pressure for months at a time. Losing more than around 0.2–0.3 bar over a month, or needing a top-up more than a couple of times a year, is a sign that something is wrong. Frequent pressure loss is almost always caused by a leak somewhere in the system — including very slow pinhole leaks — and should be investigated by an engineer rather than masked by regular repressurising.
Could a faulty pressure relief valve or expansion vessel cost a lot to fix?
Replacing a PRV or refilling/replacing an expansion vessel is typically a straightforward job for an engineer and usually falls within the £90–£320 range including labour. In rare cases where a heat exchanger is found to be leaking, costs can be considerably higher — potentially £400–£600 or more — but this is uncommon and would normally be identified during a proper leak-detection survey before any expensive parts are ordered.
Will repressurising the boiler affect my warranty?
No — topping up the system pressure using the filling loop and resetting the boiler are both actions described in the Biasi user manual as normal homeowner tasks. Carrying them out will not void your warranty. Only opening sealed gas-carrying components, the combustion chamber, or the PCB enclosure without Gas Safe authorisation could affect warranty cover.