Potterton Assure E135 fault code: what “internal error” means

If your Potterton Assure displays E135, the official manufacturer description is simply “Internal error.” Baxi lists this code for the model group that includes Potterton Assure Combi and System boilers.

The short wording is important. E135 does not name a failed component and it does not automatically mean the main circuit board needs replacing. It tells you that the boiler’s controls have detected an internal problem they cannot resolve through normal operation, so professional testing is needed if the code remains or returns.

Why the code is deliberately broad

A modern boiler supervises several processes before and while it produces heat. It checks signals, timings, safety conditions and whether commands have completed as expected. “Internal error” means the control system has stopped at this broad level rather than reporting one of the more specific public fault descriptions.

The display cannot show which internal check failed, whether the event was temporary or which test an engineer should perform first. Turning E135 into a definite claim about a circuit board, sensor, wiring loom or software setting would be guesswork.

What you may notice

The boiler may stop and show E135, leaving the home without heating, hot water or both. It may happen immediately after start-up, during a demand or after a brief electricity interruption. The timing can be useful, but it does not prove the cause.

Record:

• the exact E135 code and any other display symbol;
• whether heating, hot water or both were affected;
• what the boiler was doing immediately beforehand;
• whether the electricity supply flickered or was switched off;
• whether the boiler or heating controls were worked on recently;
• whether one reset permitted by the user guide cleared the code;
• how quickly E135 returned, if it did.

A clear sequence of events is more useful to an engineer than a suggested failed part.

Is E135 a circuit-board fault?

Not necessarily. A control board is involved in monitoring boiler operation, but E135 does not say “PCB fault”. The same manufacturer table has separate descriptions for some communication and synchronisation problems. That is a good reason not to replace the broad E135 wording with a more specific diagnosis.

An engineer must inspect the fault history and test the boiler according to the correct Assure documentation. Only then can they decide whether the issue involves a control, connection, supply condition or another internal process.

Can you reset a Potterton Assure E135?

Follow only the reset procedure in the user guide for your exact Assure model. If there is no smell of gas, carbon-monoxide alarm, visible damage or leak and the guide permits a reset, one attempt may show whether the event was temporary.

If E135 remains or returns, stop resetting and arrange repair. Repeatedly clearing the display is not the same as correcting the problem. It can also make an intermittent pattern harder to describe.

Safe checks that stay outside the casing

Confirm that the property has a stable electricity supply and that the normal external boiler switch and controls have not been turned off accidentally. Look at the display and note the pressure shown, but do not change settings simply because E135 is present.

If a separate room thermostat has an obvious blank display, record that too. Do not start pairing controls, removing receivers or altering wiring unless the exact control’s homeowner guide tells you to complete a simple user action. E135 is an internal boiler code, so an unrelated app or Wi-Fi issue should not be assumed to be the cause.

When safety warnings take priority

E135 does not itself mean there is a gas leak or carbon-monoxide release. However, any real warning sign takes priority over ordinary troubleshooting.

If you smell gas, turn off the supply at the meter only if safe, open doors and windows, avoid flames and electrical switches, leave the property and call the National Gas Emergency Service on 0800 111 999 from a safe place.

If a carbon-monoxide alarm sounds, move everyone into fresh air. Symptoms can include headache, dizziness, nausea, weakness, confusion, chest pain and breathlessness. Seek medical help, and call 999 if anyone is seriously unwell. Do not use the boiler again until it has been checked.

Why an engineer needs to investigate

A Gas Safe registered engineer can use the appliance history, approved service information and safe electrical checks to narrow down the internal error. Depending on the evidence, they may need to assess power quality, internal connections, controls, communication between components and safety functions.

Those checks can involve live electricity and the sealed boiler casing. Homeowners should not test voltage, continuity or resistance, move connectors, enter service menus, change parameters or replace a circuit board based on the code alone.

What not to do

• Do not remove the boiler case.
• Do not assume E135 means the PCB has failed.
• Do not test or alter internal wiring and connectors.
• Do not enter installer menus or change parameters.
• Do not repeatedly reset a returning code.
• Do not ignore a gas smell, carbon-monoxide alarm, leak or visible damage.

When to book repair

Arrange professional repair when E135 will not clear through the one permitted reset, when it returns or when heating and hot water are unreliable. Give the engineer the exact model, code, timing and any recent supply interruption. That is enough useful information without trying to diagnose the internal error yourself.

Quick answers

What does Potterton Assure E135 mean?

The manufacturer lists E135 as “Internal error”. It is a broad control-system fault, not a component diagnosis.

Does E135 mean the PCB must be replaced?

No. The code alone does not prove that the PCB or any other particular part has failed.

Can I reset the boiler?

Use one reset only if the exact model’s user guide permits it and no emergency warning is present.

Can a Wi-Fi problem cause E135?

Do not assume so. E135 is an internal boiler error, while an app connection can fail independently.

Who should repair it?

A suitably qualified Gas Safe registered engineer should investigate a persistent or returning E135 code.