Main E119 Fault Code: Low Water Pressure Error
The E119 fault code indicates that your Main boiler has detected water pressure that has dropped too low to operate safely — typically at or below 0.5 bar. Once the internal pressure sensor registers this, the boiler locks out and displays E119 as a protective measure. Note that pressing the reset button will not clear this fault; the pressure must be restored first. On some displays, the code appears as 'E1' followed by '19'.
General guidance only — not a substitute for professional advice. 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.
What does the Main E119 fault code mean?
The E119 fault code indicates that your Main boiler has detected water pressure that has dropped too low to operate safely — typically at or below 0.5 bar. Once the internal pressure sensor registers this, the boiler locks out and displays E119 as a protective measure. Note that pressing the reset button will not clear this fault; the pressure must be restored first. On some displays, the code appears as 'E1' followed by '19'.
Common causes
- Low system pressure after bleeding radiators Common
Bleeding radiators releases trapped air but also allows water to escape the sealed system. If the pressure is not topped up afterwards, it can drop well below the 1 bar minimum and trigger an E119 lockout. This is one of the most frequent causes of this fault.
- Gradual natural pressure loss Common
Sealed heating systems lose small amounts of pressure over time due to thermal expansion and contraction cycles and the slow release of microscopic air pockets. This process is slow — typically taking several months — but can eventually cause pressure to dip below the safe threshold.
- Leak in the heating system Common
A leak anywhere in the system — at radiator valves, pipe joints, or concealed pipework beneath floors or behind walls — will cause pressure to drop repeatedly. Signs to look for include damp patches near pipework, rust marks on radiators or valves, and the need to repressurise more than once in a short period.
- Faulty expansion vessel or pressure relief valve Sometimes
The expansion vessel absorbs pressure fluctuations as water heats and cools. If it loses its charge or fails, pressure can swing erratically and drop too low. Similarly, a pressure relief valve that has started to weep or discharge water will cause ongoing pressure loss that no amount of topping up will permanently fix.
- Internal boiler leak or worn seals Sometimes
Seals, O-rings, and internal pipework connections inside the boiler itself can deteriorate over time. A slow internal drip may be invisible from outside but will steadily reduce system pressure and trigger repeated E119 faults.
- Faulty pressure sensor or gauge Rare
If your pressure gauge reads above 1 bar but the boiler still shows E119, or vice versa, either the sensor or the gauge itself may be giving a false reading. A failed sensor can trigger a lockout even when actual system pressure is fine.
How to fix it
- Check the pressure gauge on the boiler DIY safe
Look at the pressure gauge on the front of your boiler. A healthy cold-system pressure sits between 1.0 and 1.5 bar. If it reads below 1 bar — or the needle is pointing towards zero — low pressure is almost certainly the cause of your E119 fault.
- Repressurise the system via the filling loop DIY safe
Turn the boiler off and allow it to cool for at least 30 minutes. Locate the filling loop — usually a braided metal hose with two valves found beneath the boiler. Ensure both ends are securely connected, then slowly open both valves to allow mains water into the system. Watch the pressure gauge rise and close both valves once the needle reaches 1.0–1.5 bar. Some Main and Baxi boilers have an Easy-Fill lever instead: look for a small green lever beneath the boiler, press it down to add water, and release it when the gauge enters the green zone around 1 bar.
- Reset the boiler DIY safe
Once pressure has been restored to the correct level, turn the boiler back on and press the reset button. Unlike many other faults, E119 cannot be cleared by resetting alone — the pressure must be corrected first. The boiler should now fire up normally.
- Monitor the pressure over the following days DIY safe
Keep an eye on the pressure gauge over the next 48–72 hours. If it remains stable, the issue was likely a one-off pressure drop, possibly after bleeding radiators. If the pressure falls again within a day or two, there is likely a leak or a component fault that needs professional investigation — do not keep repressurising as a workaround.
- Check for visible leaks around radiators and visible pipework DIY safe
Walk around your home and inspect radiator valves, pipe joints, and any exposed pipework for signs of moisture, rust staining, or damp patches on walls or ceilings. Even a slow weep from a valve can cause repeated pressure loss. If you find a leak, turn off the boiler and contact a Gas Safe registered engineer.
- Call a Gas Safe registered engineer Gas Safe engineer
If pressure continues to drop after repressurising, if you cannot locate a visible leak, or if the boiler shows E119 despite the gauge reading above 1 bar, you need a Gas Safe registered engineer. They can pressure-test the system to locate hidden leaks, inspect internal components such as the expansion vessel, pressure relief valve, and seals, and replace a faulty pressure sensor if required. Do not attempt to work on any internal boiler components yourself.
Parts you may need
- Pressure sensor / water pressure switch · from £22
- Expansion vessel (replacement or recharge) · from £45
- Pressure relief valve · from £18
- Filling loop assembly · from £14
- Internal boiler seals and O-ring kit · 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
Why won't my Main boiler reset after getting an E119 fault?
E119 is one of a small number of fault codes that cannot be cleared with the reset button alone. The boiler has locked out because system pressure has dropped too low, and it will not restart until that pressure is restored. Repressurise the system to between 1.0 and 1.5 bar via the filling loop, then press reset. If the boiler still does not clear the fault, the pressure sensor itself may be faulty and will need a Gas Safe engineer to diagnose.
How often should I need to top up my boiler pressure?
In a healthy sealed system, you should rarely need to repressurise — perhaps once or twice a year at most. If you find yourself topping up the pressure more frequently than that, particularly more than once a month, this is a strong indicator that there is a leak somewhere in the system. Repeatedly repressurising without finding and fixing the root cause can mask a worsening problem, so it is worth having a Gas Safe engineer carry out a pressure test to trace the source.
Could the E119 fault be caused by a faulty sensor rather than actual low pressure?
Yes, although this is less common. If your boiler's pressure gauge appears to read a healthy 1 bar or above but you are still seeing E119, the fault may lie with the pressure sensor rather than the system pressure itself. Conversely, if the gauge reads normal but the sensor is accurate and the gauge is faulty, the pressure may genuinely be low despite what the display shows. Either way, a faulty sensor or gauge needs to be diagnosed and replaced by a Gas Safe registered engineer. The pressure sensor itself is a relatively affordable part — typically around £15–£30 — so the repair bill is usually modest once labour is added.
Can a failing expansion vessel cause repeated E119 faults?
Yes. The expansion vessel contains a pressurised air charge that cushions the system as water expands when heated. Over time, the air charge can be lost, causing the pressure relief valve to discharge water every time the boiler fires — meaning the system loses pressure repeatedly. If your boiler pressure is consistently fine when cold but drops after the heating has run, or if you notice water occasionally dripping from the pressure relief valve discharge pipe outside, an expansion vessel issue is a likely culprit. Recharging or replacing the expansion vessel typically costs £120–£250 including labour.