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Potterton boiler error codes

15 codes that Potterton (Baxi Heating UK) publishes for its boilers, each with what it means, the likely cause, what you can safely check and when to call a Gas Safe registered engineer. Tap your code:

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone. Anything else is for a Gas Safe registered engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999. Codes that need one are marked Gas Safe engineer.

Read this first

Potterton is a Baxi Heating UK brand: potterton.co.uk now forwards to baxi.co.uk, and Potterton’s user guides are published by Baxi Heating UK. Which code list applies depends on the boiler. This page follows the 2017 user guide for the Ultra System (12 to 28 kW), which shows a plain number with a sign beside it: a spanner means the fault cannot be reset by you, and the reset sign R means you may clear it with the reset button. Its table lists 21 codes. Fifteen are explained below; six carry exactly the fault names of codes already explained on the Baxi boiler page and are linked there instead of repeated. The Titanium Combi and Promax Combi do not use these numbers: their user guides print Baxi’s own nine-code E-table (E20 to E160) word for word.

118 Water pressure too low

What it means
The primary (heating) water pressure is below 0.5 bar, the minimum the boiler works at. The guide also calls it E118.
Likely cause
Water lost from the heating system; the guide says a pressure below 0.5 bar may mean a leak.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Read the pressure gauge. With the system cold and the boiler off it should be at least 0.5 bar; running, it is normally 1.0 to 1.5 bar and should not go above 2.5.
  • Repressurise with the filling loop: fit the temporary filling pipe between the two isolating taps and tighten both nuts, open one tap fully, then open the second slowly while watching the gauge. Close both taps at 1 to 2 bar, then disconnect the pipe and keep it safe.
When to call a Gas Safe registered engineer
If you have to repressurise regularly, the guide says a fault or leak is indicated: seek advice from your installer or a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

117 Water pressure too high

What it means
The primary (heating) water pressure is too high. The guide says a pressure of 3 bar or more is a fault (shown as E117), and the safety pressure relief valve opens at 3 bar.
Likely cause
Too much water or pressure in the sealed heating system — for example a filling loop left open.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Read the pressure gauge: 3 bar or more confirms it. If you have just used the filling loop, make sure both of its taps are closed.
When to call a Gas Safe registered engineer
Contact your installer or a Gas Safe registered engineer as soon as possible — the guide calls this important.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

09 Gas valve connection cable

What it means
The boiler has found a fault in the cable that connects its gas valve.
Likely cause
The gas valve cable or its connection inside the boiler.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

15 Gas valve fault

What it means
The boiler has found a fault in its gas valve.
Likely cause
The gas valve, a sealed part inside the boiler.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

28 Flue sensor fault

What it means
Flue NTC fault: the temperature sensor in the flue has failed or gives no reading. On this boiler it is named only as a sensor fault, unlike Baxi’s E28, which also covers a blocked flue or condensate.
Likely cause
The flue temperature sensor (NTC) or its wiring.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

40 Heating return sensor fault

What it means
Central heating return NTC fault: the sensor on the water coming back from the radiators has failed or gives no reading.
Likely cause
The return temperature sensor (NTC) or its wiring.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

55 Calibration required

What it means
The boiler’s control needs to be calibrated.
Likely cause
The guide names the fault only; calibration is part of the engineer’s setting up of the boiler.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

109 Pre-circulation fault

What it means
A fault found while the pump was circulating water before the burner lit.
Likely cause
The guide names the fault only; it concerns the water moving through the boiler.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Read the pressure gauge; if it is below 0.5 bar, see 118.
  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

128 Flame failure

What it means
The boiler lost its flame, or did not detect one.
Likely cause
The guide names the fault only; with 133, 134 and 135 it is one of the Ultra System’s gas and flame codes.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Make sure the gas supply to the boiler has not been turned off.
  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

134 Gas valve open without gas

What it means
Elapsed time: the gas valve stayed open for too long without gas reaching the burner.
Likely cause
No gas arriving while the valve was open — a supply turned off or interrupted, or a fault in the gas path.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Make sure the gas supply to the boiler has not been turned off.
  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

135 Gas supply interrupted (internal error)

What it means
Interruption of the gas supply, reported as an internal error of the boiler’s control.
Likely cause
The gas supply to the burner stopped; the guide does not say more.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Make sure the gas supply to the boiler has not been turned off.
  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

154 Flow and return sensor test failed

What it means
The boiler’s check of its flow and return temperature sensors did not pass.
Likely cause
The flow or return sensor (NTC), or the water flow between them.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

270 Circulation fault (dry fire)

What it means
The boiler found that it was heating without enough water circulating through it — a dry-fire condition.
Likely cause
Too little water moving through the heat exchanger.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Read the pressure gauge; if it is below 0.5 bar, see 118.
  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

321 Hot water sensor fault

What it means
Hot water NTC fault: the temperature sensor on the hot-water side has failed or gives no reading.
Likely cause
The hot water temperature sensor (NTC) or its wiring.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

384 False flame

What it means
The boiler detected a flame when there should be none.
Likely cause
The guide names the fault only; the flame detection is a sealed part.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • If the display shows the reset sign R beside the code, press the reset button. If it shows the spanner instead, the guide says you cannot reset it.
When to call a Gas Safe registered engineer
If it does not clear, shows the spanner, or keeps coming back, contact your installer, annual service provider or Baxi Customer Support (0344 871 1545) for a Gas Safe registered engineer.

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

Codes explained on the Baxi boiler page

Six of the Ultra System’s codes carry the same fault name as a code in Baxi’s table, so they are explained once, on the Baxi page. The Ultra System shows them without the E (110, not E110) and clears an R fault with its reset button rather than a selector switch; a spanner beside the code still means it is not yours to reset. The Titanium Combi and Promax Combi use exactly Baxi’s nine-code table and wording, so for those boilers read the whole page: Baxi boiler error codes.

  • 20 Central heating NTC fault — the same fault name as Baxi E20
  • 110 Safety thermostat operated — the same fault name as Baxi E110
  • 125 Circulation fault (primary) — the same fault name as Baxi E125
  • 130 Flue NTC operated — the same fault name as Baxi E130
  • 133 Interruption of gas supply or flame failure — the same fault name as Baxi E133
  • 160 Fan or fan wiring fault — the same fault name as Baxi E160

Source: Potterton (Baxi Heating UK), Ultra System user guide, 12–28 kW (2017): 6.1 list of error codes, 4.1 system pressure, 4.2 re-pressurising Checked 2026-09-29.

A code that is not listed here

Potterton’s heat-only Titanium Heat shows faults as the number of flashes of a green or red status light, not as a code. For a code that is not in its table, or a fault that appears often, the Ultra System guide says to contact your installer, annual service provider or Baxi Customer Support on 0344 871 1545.

We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.

Related pages

Source

Every code on this page comes from these pages, published by Potterton (Baxi Heating UK) and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.