Johnson & Starley 8 Fault Code: Causes, Fixes & Repair Costs

Common causes

• Thermista-stat accidentally set to Summer Airflow mode Common

  The Johnson & Starley Thermista-stat room thermostat has a 'Summer air circulation' position at one end of its dial. If this has been selected — often by accident — the fan will run continuously regardless of room temperature, triggering fault code 8. This is the most common and simplest explanation, and costs nothing to resolve if that is all it is.

• Faulty Thermista-stat Common

  If the thermostat setting is confirmed correct but the fan still runs permanently, the Thermista-stat itself may have failed internally. A Gas Safe engineer can isolate the thermostat from the wiring circuit and carry out a terminal test to confirm whether the room stat or the control module is at fault.

• Wiring fault between Thermista-stat and Economaire module Sometimes

  Loose terminals, chafed wires, or a damaged wiring loom connecting the Thermista-stat to the Economaire module can send incorrect signals to the control module, producing the same fan-running-permanently symptom or causing incorrect voltage readings at the module terminals.

• Failed Economaire control module Sometimes

  If terminal voltage checks at the module show incorrect readings and the wiring and thermostat have been ruled out, the Economaire control module itself has most likely failed. Module failures can manifest in several ways — no display, failure to ignite the burners, or the fan running without stopping. Replacement of the module is the prescribed fix at this stage.

• Faulty fan or limit thermostat Rare

  A failing fan and limit stat can contribute to overlapping fault conditions on the Economaire. Although display code L is its primary indicator, a deteriorating limit stat can affect the module's voltage readings and interact with fault code 8 in older units.

How to fix it

1. Check the Thermista-stat dial position DIY safe

   Look at the Johnson & Starley Thermista-stat (the room thermostat unit) and confirm its dial is not turned to the Summer air circulation position, which is typically at the extreme end of the dial's travel. If it has been set there, return it to a normal heating position and observe whether the fan stops and the appliance resumes normal operation. This simple check costs nothing and resolves the fault in a number of cases.

2. Reset the appliance (up to 2–3 times) DIY safe

   If the thermostat position looks correct and the appliance remains in fault, attempt a reset using the reset button or by switching the appliance off at the wall, waiting around 30 seconds, and switching it back on. Attempt this no more than two or three times. If the fault code 8 returns each time, further investigation by an engineer is required — repeated resets without resolving the underlying cause will not fix the fault.

3. Check your gas supply is on DIY safe

   Ensure the gas isolation valve serving the appliance is open and, if you have other gas appliances in the home (such as a hob or gas fire), confirm they are working normally. If other appliances are also not receiving gas, contact your gas supplier rather than attempting any work on the boiler.

4. Carry out terminal voltage checks at the Economaire module Gas Safe engineer

   A Gas Safe registered engineer will measure the voltage at terminals 5 and 6 (air heater circuit) and terminals 8 and 9 (water circulator circuit) on the Economaire module. Incorrect voltages at these terminals indicate a module fault. The engineer will also link terminal 8 to the TEST terminal to establish whether isolating the Thermista-stat stops the fan — this determines whether the fault lies with the thermostat wiring or the module itself.

5. Test and replace the Thermista-stat if confirmed faulty Gas Safe engineer

   If the engineer's terminal tests indicate the Thermista-stat is the source of the fault — either through internal failure or damaged wiring — they will replace the stat and retest the system. This is a significantly more cost-effective outcome than module replacement and should always be confirmed before the module is condemned.

6. Replace the Economaire control module if required Gas Safe engineer

   If terminal voltage readings remain incorrect after the Thermista-stat and wiring have been ruled out, the Economaire control module must be replaced. Specialist engineers familiar with the Economaire range often carry a replacement module. Note that on older units, sourcing the correct module can take time, so parts availability should be discussed with the engineer at the outset.

7. Book a Gas Safe registered engineer Gas Safe engineer

   All diagnostic and repair work beyond the simple thermostat setting check and reset described above must be carried out by a Gas Safe registered engineer. You can find a registered engineer at gassaferegister.co.uk. Given that the Economaire is a specialist warm air unit, try to source an engineer with prior experience of the Johnson & Starley Economaire range if possible.

Parts you may need

• Johnson & Starley Thermista-stat room thermostat · from £80
• Economaire control module (PCB) · from £220
• Fan and limit thermostat · from £55
• Wiring loom / thermostat cable · 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 £120–£400, depending on the underlying cause.

Frequently asked questions