Potterton E119 Fault Code: Low Water Pressure
The E119 code appears on Potterton boilers when the system water pressure has dropped too low — typically below 0.5 bar — for the boiler to operate safely. Once the pressure sensor detects this shortfall, the boiler locks out and displays E119 to prevent damage to internal components. You may also see this displayed as E-119, E1 19, or similar spacing variations; they all refer to the same fault. Normal operating pressure for most Potterton systems should sit between 1.0 and 1.5 bar when cold.
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 Potterton E119 fault code mean?
The E119 code appears on Potterton boilers when the system water pressure has dropped too low — typically below 0.5 bar — for the boiler to operate safely. Once the pressure sensor detects this shortfall, the boiler locks out and displays E119 to prevent damage to internal components. You may also see this displayed as E-119, E1 19, or similar spacing variations; they all refer to the same fault. Normal operating pressure for most Potterton systems should sit between 1.0 and 1.5 bar when cold.
Common causes
- System pressure has naturally dropped over time Common
Heating systems slowly lose a small amount of pressure over months of use. Bleeding radiators without topping the system back up afterwards is one of the most common reasons pressure dips below the safe threshold and triggers E119.
- Water leak in the heating system Common
A leak on a radiator valve, a pipe joint, or a section of pipework allows water to escape, gradually reducing system pressure. If you find yourself needing to top up the pressure repeatedly every few weeks, a leak is the most likely explanation.
- Faulty or weeping pressure relief valve (PRV) Sometimes
The PRV is designed to release water when pressure gets dangerously high. If it develops a fault or starts to weep, water drips away continuously — often exiting through the condensate or overflow pipe outside — causing pressure to fall steadily.
- Waterlogged or failed expansion vessel Sometimes
The expansion vessel absorbs pressure changes as water heats up and cools down. When its internal membrane fails, the vessel can no longer do its job properly, leading to repeated pressure swings and eventually sustained low pressure readings.
- Faulty pressure sensor Rare
If the pressure gauge shows a reading above 1 bar but the boiler still displays E119, the pressure sensor itself may be sending an incorrect low-pressure signal to the PCB. Equally, a faulty pressure gauge could show a falsely healthy reading while the sensor correctly detects low pressure.
How to fix it
- Check the pressure gauge on the boiler DIY safe
Look at the pressure gauge — usually a dial or digital display on the boiler's front panel. If it reads below 1 bar, the system needs repressurising. If it reads at or above 1 bar and E119 is still showing, the fault is more likely a faulty pressure sensor or gauge, in which case skip to the final step and contact an engineer.
- Allow the boiler and pipework to cool down DIY safe
Before touching the filling loop, make sure the boiler has been off long enough for the system to cool. Working on a hot system risks scalding. Around 20–30 minutes is usually sufficient.
- Repressurise the system via the filling loop DIY safe
Locate the filling loop — typically a braided hose with one or two valves beneath the boiler. Slowly open the valve(s) to let mains water into the system. Watch the pressure gauge rise and close the valve(s) once the needle reaches approximately 1.2–1.5 bar. Do not overfill; pressure above 2.0 bar can cause the PRV to open. Consult your boiler's handbook if you are unsure which type of filling loop your model has.
- Reset the boiler DIY safe
Once the pressure is back in range, press and hold the reset button (usually marked with a flame symbol or the word 'Reset') for around 3 seconds. The E119 code should clear and the boiler should fire up normally. If it does not clear immediately, wait a minute and try once more — but avoid repeated reset attempts beyond two or three times.
- Monitor pressure over the following days DIY safe
Keep an eye on the pressure gauge over the next week or two. If pressure drops again within a short period, there is likely a leak somewhere in the system. Look for damp patches around radiator valves, visible pipework, and underneath the boiler itself. Do not keep topping up the pressure as a long-term fix.
- Contact a Gas Safe registered engineer Gas Safe engineer
If repressurising does not clear the fault, if pressure drops again quickly after topping up, if you suspect a leak you cannot locate, or if you believe the pressure sensor or PRV may be at fault, you will need a Gas Safe registered engineer to investigate and carry out any necessary repairs. Do not attempt to replace gas components, the pressure sensor, or the PRV yourself.
Parts you may need
- Water pressure sensor · from £22
- Pressure relief valve (PRV) · from £18
- Expansion vessel (replacement) · from £55
- Filling loop assembly · from £15
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–£300, depending on the underlying cause.
Frequently asked questions
Can I fix the Potterton E119 fault myself without calling an engineer?
In many cases, yes. If the fault is simply that system pressure has dropped below 1 bar, topping up the system via the filling loop is a straightforward job most homeowners can do safely. However, if the pressure drops again within a few weeks, or if the gauge already reads above 1 bar when the fault appears, you will need a Gas Safe engineer to investigate the underlying cause.
Why does my Potterton boiler keep showing E119 after I've topped up the pressure?
Recurring low pressure almost always points to a water leak somewhere in the system — this could be a dripping radiator valve, a weeping pipe joint, or a faulty pressure relief valve losing water via the overflow pipe outside your home. An engineer can pressure-test the system to pinpoint the source. Repeatedly topping up without finding and fixing the leak will not solve the problem permanently.
Will resetting the boiler clear the E119 code?
Not on its own. Unlike some fault codes, E119 is triggered by an actual low-pressure condition that the boiler's sensor is detecting. The code will only clear once the system pressure is brought back into the normal range (1.0–1.5 bar). Once you have repressurised, then reset the boiler, the fault should clear.
How much does it cost to fix a Potterton E119 fault in the UK?
If you can repressurise the system yourself, it costs nothing. If an engineer is needed — for example to repair a leak, replace a pressure relief valve, or fit a new pressure sensor — most people pay between £90 and £300 including parts and labour. A straightforward leak repair or PRV swap tends to sit at the lower end of that range. In rare cases where the expansion vessel needs replacing, costs can push slightly higher, but major component failures are not typical for this fault code.