Potterton E135 Fault Code: Causes, Fixes & Repair Costs
What does the Potterton E135 fault code mean?
The E135 code indicates an internal interruption of the gas supply — meaning the boiler itself has detected that gas is not reaching the burner as expected. Unlike a straightforward external gas supply failure (such as the meter being off or a supplier outage), E135 points firmly to a fault within the boiler's own components. In practical terms, the boiler has registered that the gas valve was open for a period of time without gas flow being confirmed, or that the valve is not functioning correctly. The boiler responds by entering lockout and shutting down completely, so it will not fire again until the underlying fault is diagnosed, repaired, and the unit is reset by a qualified engineer.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or underpowered gas valve Common
The gas valve controls the flow of gas to the burner. If it is not receiving adequate electrical power, has failed mechanically, or has corroded internal components, the boiler will not detect gas flow even when the valve opens — triggering E135. An engineer will test the valve with a multimeter to check voltage and coil resistance. If the valve itself is defective, a direct replacement is required; there is no repair option for a failed valve.
- Wiring or connection fault to the gas valve Common
Loose, corroded, or damaged wiring between the PCB and the gas valve can prevent the valve from receiving the signal or power it needs to operate correctly. This can mimic a failed valve and is worth checking before condemning the component itself, as a wiring repair is typically less costly than a full valve replacement.
- Faulty PCB (printed circuit board) Sometimes
The PCB is the boiler's control hub and sends the electrical commands that open the gas valve. A failing PCB may not dispatch the correct signal, causing the boiler to log an internal gas supply fault. Signs of PCB trouble often include erratic boiler behaviour — random shutdowns, flickering lights, or heating and hot water failing to reach set temperatures. PCB replacement is among the most expensive repairs on a Potterton boiler.
- Internal water leak causing electrical damage Sometimes
Slow internal leaks from components such as the heat exchanger or pump can allow water to track onto electrical parts over time. This kind of gradual moisture damage can corrupt the PCB, disrupt wiring, or interfere with the gas valve's electrical supply — all of which may eventually surface as an E135 fault. An engineer will inspect the boiler casing interior for signs of damp, corrosion, or water staining.
How to fix it
- Attempt a single boiler reset DIY safe
Most Potterton boilers have a dedicated reset button on the control panel. Press and hold it for approximately three to five seconds until the boiler attempts to restart. If the E135 code clears and the boiler runs normally, monitor it closely over the next few hours. If the fault returns — or does not clear on the first reset — do not keep attempting restarts, as repeated resets without fixing the root cause can mask the problem or cause further damage.
- Check that your gas supply is working elsewhere in the property DIY safe
Before calling an engineer, confirm that other gas appliances in your home (such as a gas hob or gas fire) are working normally. If nothing gas-powered is working, the issue may be with your meter or your supplier — contact your gas network operator. If other appliances are working fine, the fault is internal to the boiler and you should proceed to call an engineer.
- Contact a Gas Safe registered engineer for diagnosis Gas Safe engineer
Because E135 relates to internal gas system components, all further investigation and repair must be carried out by a Gas Safe registered engineer. Do not attempt to open the boiler casing, adjust the gas valve, or interfere with any wiring. The engineer will use a multimeter to test the gas valve for correct voltage and coil resistance, inspect all associated wiring and connectors for damage or corrosion, assess the PCB for correct output signals, and check the boiler interior for any signs of water ingress that may have caused electrical damage.
- Arrange repair or replacement of the faulty component Gas Safe engineer
Once the engineer has identified the root cause, they will advise on the appropriate repair. A gas valve replacement typically takes around a day once the part is sourced — parts are usually available from plumbing merchants on a next-day basis. If the PCB is at fault, costs are considerably higher. For older Potterton boilers where repair quotes are approaching or exceeding £500, it is worth getting one or two new boiler installation quotes at the same time, as a modern replacement may prove more economical in the long run.
Parts you may need
- Gas valve (Potterton compatible) · from £150
- PCB (printed circuit board) · from £280
- Gas valve wiring harness / loom · from £35
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £180–£400, depending on the underlying cause.
Frequently asked questions
Is E135 on a Potterton boiler dangerous?
The boiler has already responded safely by locking out and stopping operation, so there is no immediate danger in the sense of a gas escape. However, you should not attempt to bypass the lockout or repeatedly reset the boiler without a diagnosis. If at any point you smell gas, leave the property, avoid operating any switches, and call the National Gas Emergency Service on 0800 111 999 immediately.
Can I fix Potterton E135 myself?
No. Although you can safely attempt one reset and check that your wider gas supply is functioning, the components responsible for E135 — the gas valve, its associated wiring, and the PCB — must only be worked on by a Gas Safe registered engineer. Working on gas components without registration is illegal in the UK and potentially life-threatening.
How much does it cost to fix E135 on a Potterton boiler?
For the most common repair — replacing or rewiring the gas valve — expect to pay in the region of £180 to £400 including labour. Wiring faults at the lower end may cost less if parts are minimal. A PCB replacement is more expensive and can reach £500 or above depending on the model; if your boiler is older and quotes are in that territory, it is worth comparing the cost against a new boiler installation, particularly given that new boilers typically carry a five-year or longer manufacturer warranty.
Why does my Potterton boiler keep showing E135 after a reset?
A successful reset simply clears the lockout condition — it does not fix the underlying fault. If the gas valve is failing, the wiring is damaged, or the PCB is sending incorrect signals, the boiler will detect the same problem on its next firing attempt and lock out again. Repeated resets without a repair are not a solution and may delay diagnosis. If the fault returns after one or two resets, call a Gas Safe engineer rather than continuing to reset.