Potterton E117 fault codewhat it means and how to fix it
Primary water pressure above 2.7 bar on the Potterton Promax Ultra. Usually an over-filled system or a failed expansion vessel; an engineer should let it down and find out which.
Take care
Get a Gas Safe registered engineer to look at your Potterton E117
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What does the gauge do as the heating warms up?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
Rises from normal to near 3 bar, then falls when cool
Expansion vessel. Letting water out will not fix it for long.
Engineer to recharge or replace the vessel and check the relief valve seat.
High even when cold
Over-filled, or a filling loop letting by.
Engineer to reduce the pressure and check the loop valves; do not bleed a radiator to do it yourself unless you are confident, as the water is hot.
What E117 means
The Promax Ultra is the only Potterton whose manual carries this code. Section 17.2 of its installation manual says "117 is displayed when the primary water pressure is greater than 2.7 bar" and the table calls it "Primary System Water Pressure Too High". The user guide puts it in owner terms: "If the pressure exceeds 3 bar the safety pressure valve will operate and a fault is indicated (E117 displayed). Contact your installer."
The Assure, which is otherwise the same boiler, does not list 117; its user guide simply says the safety valve will operate above 3 bar. A correction to this page: it previously attributed E117 to the Gold and Titanium ranges. Neither manual contains it — those boilers have a mechanical gauge and no high-pressure code at all — and the attribution has been withdrawn. High pressure on a sealed system has two ordinary causes.
Someone filled it too far, cold, and the heat has taken it past the limit; or the expansion vessel has lost its charge, so the water has nowhere to expand into and the gauge climbs from normal to 3 bar every time the burner runs. The second is the one that comes back after the pressure is let down, and it is the one worth paying to fix, because a relief valve that has lifted a few times seldom seals properly again.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Over-filled during a top-up | The Ultra user guide says to stop between 1 and 1.5 bar. A loop left open, or a fill done while the system was hot, ends here. | Common |
| Expansion vessel discharged | Normal cold pressure that climbs past 2.7 bar as the heating warms up and drops back when it cools is the signature. The vessel needs recharging or replacing. | Common |
| Filling loop valve passing | A permanent loop whose valve does not seal lets mains pressure creep into the heating circuit over days. The relief valve then drips outside as well. | Occasional |
| Pressure sensor fault | The Ultra parts list names a "Hydraulic Pressure Sensor" (720789001) rather than the Assure's switch. If the gauge disagrees with the display, the sensor is suspect. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£80–£300
Time on site
45 minutes
Pressure let down and vessel recharged £80–£120. Expansion vessel replaced £180–£300. Pressure relief valve £90–£160.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Expansion vessel (8 litre, sealed system)
EV-8L£35–£85Plumbing merchant
Price checked 28 September 2026
Pressure relief valve, 3 bar
PRV-3B£18–£42Plumbing merchant
Price checked 28 September 2026
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Related Potterton fault codes
- E119Get it checkedThe sealed system on a rotary-switch Potterton — Promax, Titanium, Gold, Heatmax — has dropped below half a bar. The window shows E1 and then 19. Fill to 1–1.5 bar and it clears itself.Related: water pressure
- E118Get it checkedThe digital-display Pottertons — Assure Combi, Assure System, Promax Ultra — have dropped below half a bar on the heating circuit. Repressurise to 1–1.5 bar and the boiler restarts on its own.Related: water pressure
- E133Get it checkedGas supply interrupted, ignition failed or no flame detected — every Potterton generation. Confirm the gas supply, one reset (5 s on the knob, 1–3 s on the button), and call if it returns.Related: same brand
- E110Get it checkedSafety thermostat operated — the primary water overheated — on every Potterton code display. One reset is permitted (5 s knob or 1–3 s button); a second E110 is a circulation fault for an engineer.Related: same brand
- E125Get it checkedCirculation fault (primary circuit) on every Potterton code display — the water did not warm as expected after lighting, or overshot twice. Pump, air or sludge; an engineer job after one reset.Related: same brand
- E128Get it checkedFlame failure during normal operation on the Potterton Assure and Promax Ultra: the burner was lit and went out. Resettable; recurring E128 wants an engineer.Related: same brand
Own a Potterton boiler? Save it and its codes come first next time.
Related guides
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.