Johnson & Starley 30 Fault Code: Causes, Fixes & Repair Costs

Common causes

• Blocked air filter or restricted ductwork Common

  Dust and debris accumulating in the return air filter or within the warm air ductwork is the single most common trigger for shutdowns on J&S 30-series warm air heaters. When airflow is severely restricted, the heat exchanger cannot shed heat fast enough and the overheat thermostat trips, shutting the appliance down as a safety measure. A blocked filter also forces the circulation fan to work harder, shortening its lifespan.

• Fan fault — circulation air fan or combustion air fan Common

  The J&S 30-series uses two fans: a combustion air fan (CAF) and a circulation air fan (ACF). Either can fail over time as bearings wear or accumulate debris. A tell-tale sign is grinding or screeching noise before complete failure. On the combustion side, if the CAF cannot generate a pressure differential of at least 0.48 mbar across the air pressure switch (APS), the ignition sequence will not progress. Dust on the fan blades or a mis-calibrated APS can both cause this. On the circulation side, a voltage of approximately 10 VDC should be present at the fan terminals when running at maximum — absence of this points to a PCB issue, while voltage present but the fan not running points to the ACF itself needing replacement.

• Blocked or frozen condensate drain restrictor Common

  J&S WarmCair boilers are condensing appliances and produce significant condensate. A small red plastic restrictor (approximately 2 mm internal bore) sits inside the condensate pipe where it meets the drain pump. This restrictor routinely becomes blocked with debris and must be checked at every annual service. A blockage causes condensate to back up inside the heat exchanger — in some cases filling the heat exchanger up to fan level — and triggers an automatic shutdown. In cold weather, the external condensate run can also freeze solid.

• Flame failure or ignition lockout Sometimes

  If the boiler fires but then cuts out shortly afterwards, flame failure is the likely cause. The most common reason on these appliances is a poor electrical connection between the flame sensing electrode lead and its tag — if the lead is not firmly pressed onto the tag, the control board never receives confirmation that a stable flame is present and locks the appliance out. Other contributors include fluctuating incoming gas pressure, a contaminated or cracked flame sense electrode, or wiring faults on the ESYS module.

• PCB or sensor wiring fault Sometimes

  Loose, corroded, or damaged wiring connections — particularly those on the PCB or on the gas valve's 'piggy-back' connector — can cause the control board to misread sensor signals and trigger a spurious lockout. The flue temperature sensor open-circuit error is one known example. Wiring faults of this type require a Gas Safe engineer to diagnose and rectify safely.

How to fix it

1. Identify your actual fault code using the RESET button DIY safe

   If the display shows a small 'e', press and hold the RESET button for more than one second, then release. The specific fault code will appear. Write it down and cross-reference it with the fault chart printed on the inside of the control board cover or in your appliance's installation and service manual (available at johnsonandstarley.co.uk or via ManualsLib). This will tell you — and any attending engineer — exactly which system has triggered the shutdown.

2. Check and clean the return air filter DIY safe

   Locate the return air filter grille, typically at low level on the warm air unit. Remove the filter panel and inspect the filter element. If it is clogged with dust and fluff, clean or replace it according to your manual's instructions. This is a homeowner-serviceable task, costs very little, and resolves a surprisingly high proportion of overheat shutdowns on J&S warm air heaters.

3. Check for obvious ductwork obstructions DIY safe

   Walk around your home and make sure none of the warm air supply or return air grilles are blocked by furniture, curtains, or other objects. Restricted return air is the primary cause of overheating. Do not attempt to access or modify ductwork internally.

4. Thaw a frozen condensate pipe if the weather is cold DIY safe

   If temperatures have recently dropped below zero and your boiler has stopped working, the external condensate drain pipe may be frozen. Pour warm (not boiling) water over the external pipe to thaw it, working from the boiler end outwards. Once the blockage clears, reset the boiler as described in step 5. Insulating the pipe with lagging afterwards will help prevent a recurrence.

5. Reset the boiler (up to two or three times only) DIY safe

   Press and hold the RESET button for approximately one second as described in your manual. Allow the boiler to complete its ignition sequence. If it lights and runs normally, monitor it over the next hour. If it locks out again, do not keep resetting — repeated resets without resolving the underlying fault can mask a genuine safety issue and may cause further damage.

6. Listen for unusual fan noise before calling an engineer DIY safe

   With the boiler running (if it will), listen carefully for any grinding, rattling, or continuous screeching noise from the unit. A fan running noisily is a reliable early warning that the bearings are failing. Note this observation to relay to the engineer — it will help them diagnose the fault more quickly.

7. Contact a Gas Safe registered engineer for all further diagnosis and repair Gas Safe engineer

   All fault-finding beyond the checks above — including inspecting the combustion air fan, testing the air pressure switch, clearing the condensate restrictor internally, checking flame electrode connections, testing PCB wiring, and any gas-related work — must be carried out by a Gas Safe registered engineer. You can find a registered engineer at gassaferegister.co.uk or by calling Johnson & Starley's technical helpline on 01604 762881. Do not attempt to work on gas components, the PCB, the gas valve, or internal wiring yourself.

Parts you may need

• Circulation air fan (ACF) · from £130
• Combustion air fan (CAF) · from £145
• Air pressure switch (APS) · from £45
• Condensate drain pump · from £75
• Condensate restrictor (red plastic insert) · from £8
• Flame sense electrode · from £35
• Overheat thermostat / limit stat · from £40
• PCB / control board · from £220

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