What the E117 code means
On Baxi models that use it, including the Baxi 100 series and EcoBlue boilers, E117 is described as "primary system water pressure too high". The primary system is the sealed circuit of water that runs between the boiler and your radiators. A pressure sensor inside the boiler watches that circuit all the time. If the reading climbs above the safe working limit, the boiler shuts down and shows E117.
High pressure matters because the system has a pressure relief valve, usually set to open at 3 bar. If the pressure reaches that point, the valve dumps water outside through a copper pipe. The boiler stopping before that happens gives you a chance to find the cause.
E117 is the opposite of the low pressure codes. Newer Baxi boilers show E118 for low pressure, and older ranges use E119. Some Baxi manuals do not list E117 at all, so check the fault table for your exact model.
Common causes of E117
Overfilling after a top-up
The simplest cause is too much water going in. If the system was topped up to 2 bar or more while cold, the pressure can rise well past that when the water heats up and expands.
Filling loop left open or letting by
A filling loop valve that has not been closed fully lets mains water creep into the system. Valves can also wear and let water pass even when they look closed, which engineers call letting by.
Expansion vessel lost its charge
The expansion vessel absorbs the extra volume as water heats. If it loses its air charge, there is nowhere for the water to go, so pressure shoots up when the heating runs and falls back when it cools.
Faulty pressure sensor
If the gauge reads normal but E117 keeps showing, the sensor may be giving a false reading.
Internal leak on a combi
Less often, on a combi the plate heat exchanger can fail internally and let mains water leak into the heating side. The pressure then creeps up even with the filling loop closed.
| Cause | Typical sign | Who fixes it |
|---|---|---|
| Overfilled system | Gauge above 1.5 bar when cold, just after topping up | You, by bleeding a radiator |
| Filling loop left open | Pressure rises steadily, valve handle not fully closed | You, by closing the valves |
| Filling loop letting by | Pressure creeps up with valves closed | Gas Safe engineer or plumber |
| Expansion vessel lost charge | Pressure swings high when hot, low when cold | Gas Safe engineer |
| Faulty sensor or internal leak | E117 persists, gauge reading does not match | Gas Safe engineer |
Safe checks you can do yourself
- Switch the heating off and let the system cool, then read the gauge. Pressure is always higher when hot, so a cold reading is the one that counts.
- Check both filling loop valves are fully closed. If yours is a removable braided hose, your manual may advise disconnecting it after use.
- If the cold pressure is above 1.5 bar, bleed a radiator slowly with a radiator key and a cloth to catch the water, watching the gauge. Close the bleed valve once the reading is between 1 and 1.5 bar.
- Press reset as your manual describes, no more than two or three times.
- Check the copper relief pipe outside for drips, which show the valve has been opening.
- Note the cold pressure each day for a week. If it creeps up again, something is letting water in.
Our guide to boiler pressure that is too high covers bleeding a radiator to lower the pressure in more detail.
Do not open the pressure relief valve, remove the casing or try to recharge the expansion vessel yourself. These parts are inside the boiler or connected to it and must be checked by a Gas Safe registered engineer.
When to call a Gas Safe engineer
If you have lowered the pressure and it climbs back up within a few days, call an engineer. The same applies if the pressure swings between very high when hot and low when cold, if water is dripping from the relief pipe outside, or if the gauge reads normal but E117 will not clear. The engineer will usually check the expansion vessel charge, test the filling loop valves, check the relief valve and test the pressure sensor.
It helps to keep a short record before the visit. Note the cold reading each morning and the reading after the heating has been on for an hour. A system that jumps from 1.5 bar cold to nearly 3 bar hot points strongly to the expansion vessel. A system that creeps up day by day, even when cold, points to water getting in through the filling loop or, on a combi, through the plate heat exchanger. Giving the engineer those numbers can shorten the diagnosis considerably.
Typical repair costs in the UK
Typical ranges only. Your bill depends on your area, the model and whether parts are in stock.
| Job | Typical UK cost |
|---|---|
| Engineer call-out and diagnosis | Typically £80 to £150 |
| Expansion vessel recharge | Typically £80 to £150 |
| Filling loop valve replacement | Typically £80 to £150 |
| Pressure relief valve replacement | Typically £120 to £220 |
| Pressure sensor replacement | Typically £100 to £200 |
| Plate heat exchanger replacement (combi) | Typically £200 to £400 |
How to stop E117 coming back
When you top up, fill slowly and stop at 1 to 1.5 bar with the system cold. Close both filling loop valves firmly and check the gauge again an hour later. Checking the pressure once a month helps you spot a slow rise before the boiler locks out. A yearly service lets an engineer check the expansion vessel charge before it causes trouble. See our boiler service cost guide for what is included.