Johnson & Starley 5 Fault Code: Causes, Fixes & Repair Costs
What does the Johnson & Starley 5 fault code mean?
Fault Code 5 on Johnson & Starley appliances — displayed as 'E5' on WarmCair warm air heaters and related models such as the Economaire, QuanTec, and Reno ranges — indicates that the boiler's control board has been unable to confirm adequate combustion airflow before the ignition sequence can proceed. In plain terms, the appliance expects to see a pressure differential of at least 0.48 mBar generated by the combustion air fan (CAF), which the air pressure switch (APS) must detect before the burner is allowed to light. If that signal never arrives — whether due to a sluggish fan, a blocked flue, a contaminated venturi, or a wiring issue — the boiler locks out and displays code 5. On Economaire and similar models, codes in the 4–9 range can also be triggered by a fault in the gas control valve assembly, including the electromagnetic coil or the combustion control board that sits directly on the valve, so a Gas Safe engineer will need to verify exactly which component is responsible.
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
- Dirty or restricted combustion air fan (CAF) Common
Dust and debris can coat the fan blades or clog the restrictor fitted in the positive air hose that connects to the air pressure switch. Either problem reduces the pressure differential the fan can develop, so the APS never closes and the ignition sequence stalls. This is the single most frequent finding during fault diagnosis on WarmCair appliances.
- Contaminated or blocked venturi Common
The venturi inside the CAF assembly can become fouled over time. When this happens, the pressure signal passed to the APS is weakened even if the fan itself is spinning correctly. Engineers often find that blowing through the connecting tubes clears a partial blockage, though a proper clean or component replacement is the lasting fix.
- Condensate build-up in the heat exchanger Common
On condensing WarmCair models, condensate liquid can accumulate in the heat exchanger — sometimes reaching up to one-third of its volume — interfering with airflow and triggering fan or pressure-related faults. This is a well-documented characteristic of the WarmCair range and is often only discovered when the combustion fan is removed during a service.
- Flue blockage Sometimes
Any obstruction in the flue — a bird's nest, debris, or a deteriorated flue terminal — reduces the back-pressure the fan works against and can prevent the APS from registering adequate differential pressure. The boiler may lock out intermittently or consistently depending on the severity of the blockage.
- Faulty or mis-calibrated air pressure switch (APS) Sometimes
Over time the APS diaphragm can fatigue or the switch can drift out of calibration, meaning it fails to operate even when the fan is producing sufficient pressure. A digital manometer is the most reliable tool for distinguishing a genuine APS fault from a low-pressure fault caused by a dirty fan.
- Wiring fault between fan and PCB Sometimes
Loose terminals, corroded connectors, or wiring that has lost continuity between the combustion fan and the control board can prevent the PCB from receiving the fan's feedback signal. If 230 V is confirmed at the fan terminals but the fan does not run, the PCB itself may be at fault.
- Flame sensing error or unstable gas pressure Sometimes
A degraded flame sensor or fluctuating gas supply pressure can cause the appliance to misread combustion conditions after the burner lights, triggering a lockout that presents as code 5. On Economaire models, a fault in the gas valve coil or the combustion control board mounted on the valve can also produce codes across the 4–9 range.
- Faulty combustion air fan motor Rare
If the fan motor itself has failed, it will not run regardless of the control signal sent to it. This is less common than contamination issues but should be confirmed by checking that the correct voltage (approximately 10 VDC) is present at the fan and that the fan still fails to reach full speed before the motor is condemned.
How to fix it
- Check that gas is reaching the property DIY safe
Make sure your gas supply is turned on at the meter and that other gas appliances in the home — a hob, for example — are working normally. If there is no gas supply, contact your gas supplier rather than attempting a boiler reset.
- Reset the boiler (up to two or three times) DIY safe
Press the reset button as described in your user manual and allow the ignition sequence to complete. Occasionally, a momentary interruption in gas supply causes a nuisance lockout that clears on reset. Do not reset more than two or three times; repeated lockouts indicate a genuine fault that needs investigation.
- Check for a frozen or blocked condensate pipe (condensing models) DIY safe
In cold weather, the external condensate drain pipe can freeze solid and cause a lockout. If you can safely reach the pipe, wrapping it in warm (not boiling) water or a heat wrap can thaw it. Once clear, reset the boiler. If the pipe is not frozen or this does not apply to your model, move on.
- Arrange for a Gas Safe engineer to inspect the combustion air fan Gas Safe engineer
The engineer will check that the fan runs and reaches maximum speed, confirm that approximately 10 VDC is present at the fan terminals, and use a digital manometer to measure the pressure differential being generated. If the fan is running but not producing enough pressure, the blades and venturi will be cleaned or the fan replaced.
- Have the engineer inspect and clean the venturi and air hoses Gas Safe engineer
The connecting tubes and venturi inside the CAF assembly are a common site for contamination on WarmCair appliances. The engineer can attempt to clear a partial blockage by blowing through the tubes or, if that is ineffective, by fully cleaning or replacing the assembly.
- Have the engineer inspect the heat exchanger for condensate accumulation Gas Safe engineer
On condensing WarmCair models, the engineer will remove the burner and combustion fan to inspect the heat exchanger for condensate build-up. If significant liquid is present, it will be cleared and the drainage path checked to prevent recurrence.
- Have the engineer check the air pressure switch and wiring Gas Safe engineer
Using a manometer, the engineer will confirm whether the APS is opening and closing at the correct pressure differential (0.48 mBar). They will also inspect the wiring loom between the fan and PCB for loose connections, corrosion, or breaks in continuity.
- Have the engineer check the flame sensor and gas valve Gas Safe engineer
If airflow is confirmed to be adequate, the engineer will inspect the flame detection lead and sensor for damage or soiling, and verify that gas supply pressure remains stable during the ignition sequence. On Economaire and similar models, the gas valve coil and the combustion control board on the valve will also be tested.
- Have the engineer check the limit switch and PCB if other causes are ruled out Gas Safe engineer
If all components upstream have been checked and found satisfactory, the limit switch continuity and the PCB itself will be tested. PCB faults are less common but can produce identical symptoms when wiring and fan checks are normal.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
Fault Code 5 requires component-level diagnosis that is beyond homeowner checks. A Gas Safe registered engineer has the tools — including a digital manometer and multimeter — to pinpoint the cause safely. Note that spare parts for Johnson & Starley appliances can sometimes be difficult to source, so ask your engineer to confirm parts availability before committing to a repair.
Parts you may need
- Combustion air fan (CAF) assembly · from £150
- Air pressure switch (APS) · from £55
- Flame sensor / detection electrode · from £30
- Gas valve assembly · from £220
- PCB (main control board) · from £280
- Limit switch · from £25
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 £150–£380, depending on the underlying cause.
Frequently asked questions
Can I fix Johnson & Starley Fault Code 5 myself?
The only checks a homeowner can safely carry out are confirming the gas supply is on, attempting one or two resets, and thawing a frozen condensate pipe in cold weather. Everything else — testing the fan, measuring APS pressure differential, inspecting the heat exchanger, and checking the gas valve — requires a Gas Safe registered engineer with specialist tools. Attempting gas or electrical component work without the correct qualifications is illegal and dangerous.
Why does Fault Code 5 keep coming back after I reset it?
Repeated lockouts after resetting almost always mean a component is genuinely failing rather than a one-off nuisance trip. The most frequent culprits are a fan with dirty blades or a fouled venturi, condensate build-up in the heat exchanger on condensing models, or a deteriorating air pressure switch. Each reset without fixing the root cause puts additional wear on the ignition components, so it is worth arranging an engineer visit promptly rather than continuing to reset.
How much does it typically cost to repair Fault Code 5 on a Johnson & Starley boiler?
Most repairs that resolve this fault fall between £150 and £380, covering an engineer's diagnostic time and the cost of the most commonly replaced parts: the combustion air fan, air pressure switch, or flame sensor. If the PCB or gas valve needs replacing the bill can rise to £400–£500. A heat exchanger replacement — the most expensive scenario — can push beyond £600, at which point a full boiler replacement may be more economical, especially given that spare parts for Johnson & Starley appliances can be slow to source.
Does Johnson & Starley's 8-year warranty cover Fault Code 5 repairs?
Johnson & Starley offer an 8-year parts and labour warranty as standard on their appliances, but it is conditional on the boiler being serviced annually by a Gas Safe registered engineer. If annual servicing has lapsed, the warranty may be void. Contact Johnson & Starley directly to confirm your warranty status before commissioning a repair, as a valid warranty could cover the cost of parts or labour entirely.