Potterton E109 fault codewhat it means and how to fix it
The digital-display Pottertons' pre-ignition pump check — Assure Combi, Assure System, Promax Ultra. The flow never proved, so the burner was not lit. Bleed and check pressure; then an engineer.
Take care
Did 109 follow a top-up or repair?
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.
Yes
Air.
Bleed, top up, power cycle. Engineer if it persists.
No, it appeared on its own
Pump.
Engineer.
What E109 means
On the Assure and Promax Ultra the pre-ignition pump check is code 109, "Pre-circulation fault", the renumbered successor to the Promax family's E193. The Assure System fault-finding chart places it precisely: after the pump runs and the fan proves, if "109 flashing" appears the engineer goes to section J, and the same section handles "125 flashing after 1 min" — the post-ignition circulation test.
The two are the same problem caught at different moments. Neither installation manual puts 109 on the reset list (that list is 09, 15, 110, 125, 128, 133, 134, 135 and 384) and the Assure user guide's table shows it without the R symbol, so the owner's options are the physical ones: make sure there is water in the system, that it is not full of air, and that the pump has power. The Assure user guide's troubleshooting table covers the first two — "The water pressure is too low (< 0.5 bar). Re-pressurise the system" and the maintenance advice to vent the radiators — and stops there. A 109 that survives a top-up and a bleed is a pump or a blockage.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Pump not running | Section J tests for supply at the pump and replaces the pump assembly (7684006) or its head (7686336, listed separately for the Assure) when it has supply and does not turn. | Common |
| Air in the heat exchanger | Common after repressurising. The automatic air vent (7207776) on the pump must be free to release it. | Common |
| Restricted flow | Sludge in the exchanger or a valve closed on the primary circuit. | Occasional |
What to try yourself
Read the pressure off the display or the gauge; the Assure guide wants at least 0.7 bar. Top up if needed as described on the 118 page.
Vent every radiator with a cold band across the top, then top up again. Switch the boiler off at the spur for a minute and back on.
If 109 remains, contact your installer or Baxi Customer Support. Reset does not act on this code.
Get a Gas Safe registered engineer to look at your Potterton E109
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 it costs to fix
Typical repair cost
£0–£600
Time on site
20 minutes
Free if bleeding cures it. Pump £180–£300. Power flush £350–£600.
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.
Magnetic system filter, 22mm
MAG-22£65–£120Plumbing merchant
Price checked 28 September 2026
Baxi / Potterton / Main pump assembly
7684006£120–£240Authorised Baxi parts distributor
Price checked 28 September 2026
Baxi / Potterton / Main automatic air vent
7207776£15–£45Authorised Baxi parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Potterton fault codes
- 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: overheat and circulation
- 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: overheat and circulation
- E130Get it checkedFlue NTC operated — the flue gas got too hot — on every Potterton code display. Reset once as the user guide allows; if it returns the heat exchanger or flue needs an engineer.Related: overheat and circulation
- E193Get it checkedThe rotary-switch Pottertons' pre-ignition pump check has failed: the pump ran and the flow never proved. Same causes as E125; no owner reset is offered.Related: overheat and circulation
- E270Get it checkedCirculation fault (dry fire) on the Potterton Assure and Promax Ultra: the burner lit with too little water passing the heat exchanger. Not resettable by the owner; engineer.Related: overheat and circulation
- 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: 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.