Johnson & Starley E05 Fault Code: Causes, Fixes & Repair Costs
What does the Johnson & Starley E05 fault code mean?
The E05 code appears on Johnson & Starley boilers — including the Quantec, Reno HE, and WarmCair ranges — when the PCB detects a problem with the flue fan. This means the fan has either failed to start, is running well below its required speed, or has stopped mid-cycle. Because the fan is responsible for expelling harmful combustion gases safely through the flue, the boiler will shut itself down and lock out rather than risk those gases remaining inside the appliance or your home. A reset may clear the lockout temporarily, but if the underlying fan fault remains, E05 will return. Diagnosis and repair must be carried out by a Gas Safe registered 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
- Worn fan bearings or failing motor Common
Over time, the fan motor's bearings wear and the windings can deteriorate, causing the fan to spin too slowly or fail to reach the speed the PCB expects. A telltale sign engineers look for is a fan that rotates sluggishly but picks up briefly when spun by hand — a classic indicator of bearing wear rather than a complete motor failure.
- Fan not receiving correct voltage from the PCB Common
If the wiring or control circuit is interrupted, the fan may receive insufficient voltage to reach full speed. Engineers check for approximately 10 VDC across the fan connector (blue negative, yellow positive). If voltage is present at the correct level but the fan still underperforms, the fan unit itself is at fault; if voltage is absent or low, attention shifts to the wiring or PCB.
- Wiring fault between the fan and the PCB Sometimes
Loose, corroded, or damaged connections along the loom that runs from the main controller (MMI) to the fan can interrupt the signal the PCB uses to monitor fan speed. On the WarmCair range in particular, the fault-finding procedure specifically directs engineers to check continuity of this wiring as an early step.
- PCB failure Rare
A faulty PCB can misread or fail to send the correct control signal to the fan, triggering an E05 even when the fan itself is in good condition. This is considered less likely unless there has been water ingress or evidence of electrical damage on the board. On some older Johnson & Starley models, the electronic control panel and the fan speed controller are replaced as a paired unit, which can be a significant cost.
How to fix it
- Reset the boiler once or twice DIY safe
Press the reset button and allow the boiler to restart. If E05 clears and the boiler runs normally, monitor it closely over the next few hours. If the fault returns within a short period, do not keep resetting — repeated resets without fixing the root cause will not help and may mask important symptoms for the engineer.
- Check that your gas supply is working DIY safe
Confirm that other gas appliances in your home (hob, gas fire) are working normally. If they are not, contact your gas supplier. If they are working fine, the issue is specific to the boiler's fan circuit rather than the gas supply.
- Visually inspect the flue terminal outside (do not touch) DIY safe
From a safe distance, check that the external flue outlet is not physically blocked by debris, a bird's nest, or heavy snow. A blocked flue can cause pressure build-up that stresses the fan, though E05 points more specifically to a fan speed issue than a simple blockage.
- Engineer to test fan voltage and speed Gas Safe engineer
A Gas Safe engineer will measure the DC voltage at the fan connector and use the boiler's diagnostic mode to confirm whether the fan is reaching the required speed. This pinpoints whether the fault lies with the fan motor itself, the wiring loom, or the PCB's output circuit.
- Engineer to inspect and test the wiring loom Gas Safe engineer
The engineer will check all connections between the MMI controller and the fan for security and continuity, looking for corrosion, chafing, or loose terminals that could interrupt the fan's speed-feedback signal to the PCB.
- Engineer to replace the fan unit if confirmed faulty Gas Safe engineer
If voltage is confirmed at the correct level but the fan still fails to reach operational speed, the fan assembly is replaced. On some models it may be possible to replace only the motor rather than the complete fan unit, which can reduce parts costs somewhat.
- Engineer to assess and replace PCB if required Gas Safe engineer
If the fan tests as healthy but the fault persists, the PCB is investigated. On certain older Johnson & Starley models the electronic control panel and fan speed controller must be replaced as a matched pair. Your engineer will advise whether the repair cost is proportionate to the boiler's age and condition.
Parts you may need
- Flue fan / air circulation fan (ACF) assembly · from £150
- Fan motor (where supplied separately) · from £80
- PCB / main control board · from £280
- Wiring loom (fan to PCB) · 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 £220–£380, depending on the underlying cause.
Frequently asked questions
Can I fix a Johnson & Starley E05 fault myself?
No. While you can safely reset the boiler once or twice and check your gas supply is on, any further work — testing voltages, inspecting internal wiring, or replacing the fan or PCB — must be done by a Gas Safe registered engineer. Johnson & Starley's own fault-finding documentation is written specifically for registered engineers, and working on a gas appliance without Gas Safe registration is illegal as well as dangerous.
How much does it cost to fix an E05 fan fault on a Johnson & Starley boiler?
Most homeowners pay in the region of £220–£380 all-in for a fan replacement including labour. The fan part itself typically costs £100–£200 depending on the model, with engineer labour on top. If the PCB also needs attention — which is less common — a new board can add £180–£400 to the bill, and on some older Johnson & Starley models the control panel and fan speed controller must be replaced as a pair, which can push costs higher still. In that situation your engineer may suggest weighing up the repair cost against replacing an ageing boiler.
Why does my Johnson & Starley boiler show E05 then go to another lockout code?
This is a recognised pattern reported by engineers on the Reno HE range. E05 indicates the fan speed fault; after a set number of failed restart attempts the boiler then triggers a secondary lockout code (such as E01, the ignition lockout). The second code is a consequence of the first — the boiler could not establish a safe flue flow, so ignition was never permitted and the unit locked out fully. Treating the fan fault will resolve both codes.
Is an E05 on a Johnson & Starley boiler dangerous?
The boiler has shut itself down precisely because it detected the fan was not working correctly — this is the safety system doing its job. Do not attempt to bypass the lockout or force the boiler to fire. Leave it locked out and call a Gas Safe engineer promptly, particularly during cold weather, to avoid the risk of harmful flue gases not being expelled properly if the boiler were to fire with a faulty fan.