Potterton E103 fault codewhat it means and how to fix it
Codes 103, 104, 107 and the word "Bat" on the Potterton Assure: the user guide names them only to say contact your installer or Baxi Customer Support. They concern the safety board's battery.
Take care
Get a Gas Safe registered engineer to look at your Potterton E103
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 is on the display?
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.
"Bat"
Battery warning. The boiler may still run for now.
Book the battery change before it becomes 103.
103, 104 or 107
Safety board stopped the boiler.
Installer or Baxi Customer Support; no reset applies.
What E103 means
The Assure Combi user guide lists twenty codes in its table and then adds a line about four displays that are not in it: "For 103, 104, 107 & 'Bat' please contact your installer, annual service provider or Baxi Customer Support." That is the whole of what Potterton's document says. It does not describe them and it does not offer the Reset button for them; they sit outside the R group.
What they mean comes from the other badge on the same platform: the Assure is the Baxi 600 with a Potterton fascia, and Baxi's professional error-code page for the 600 describes 103 as the Safety Assist battery exhausted, 104 as a faulty Safety Assist PCB and 107 as the two boards not synchronised, with "Bat" the early warning that the cell is running down. Safety Assist is a second circuit board with a battery of its own, there so that the boiler's safety monitoring survives a mains interruption, and the main board refuses to run without it once the cell is flat.
None of that is in a Potterton-badged document, which is why this page attributes it to Baxi rather than to Potterton. The Potterton instruction is enough on its own: these are not codes to clear, the cell is not something the owner changes, and the number to ring is on the guide. The Assure System user guide and the Promax Ultra do not mention them.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Safety board battery exhausted ("Bat", then 103) | The warning shows first; the boiler stops once the cell is flat. Changing it means opening the casing, so it is an engineer's visit. | Common |
| Safety board fault (104) | The second circuit board itself has failed its self-check. An engineer diagnoses it by substitution and the board is replaced as a unit. | Occasional |
| Boards out of step (107) | Main board and safety board no longer agree with each other, usually because one was changed and the pairing step was missed. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£60–£320
Time on site
45 minutes
Battery replacement at a call-out £60–£120. Safety Assist board £150–£320.
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.
Baxi / Potterton / Main main PCB
£150–£320Authorised Baxi parts distributor
Price checked 28 September 2026
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Related Potterton fault codes
- E83Usually simple to fixCommunication error on the Potterton Assure and Promax Ultra: the board has lost contact with a connected control such as an OpenTherm room unit. Check the control and its wiring first.Related: electronics and power
- E55Usually simple to fixCalibration required on the Potterton Promax Ultra — shown after the gas valve or board is replaced until the engineer runs the calibration routine. Not a fault an owner will meet unprompted.Related: electronics and power
- E131Usually simple to fixInterruption of power supply while in fault mode — the Potterton Promax Store only. The power went off while another code was showing. Restore power, read the code that follows.Related: electronics and power
- 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
- 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
- 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: 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
- Manufacturer support portal
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.