Johnson & Starley E34 Fault Code: Causes, Fixes & Repair Costs
What does the Johnson & Starley E34 fault code mean?
E34 on a Johnson & Starley unit is a low power supply lockout: the mains voltage reaching the appliance has dropped below the threshold the control board requires for reliable operation. Gas valves, ignition circuits and safety relays all have minimum-voltage requirements — operate them undervoltage and their behaviour becomes unpredictable — so the controller shuts down rather than run marginal. The cause is usually outside the unit: a genuine supply dip in the property or wider network, a poor connection at the fused spur or in the appliance's supply wiring adding voltage drop, or, less often, a fault in the board's own power section misreading the supply.
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
- Genuine supply dip or brownout Common
Local network dips — often evening peaks or shared-supply properties — pull the voltage under threshold. If lights dim at the same time, the supply is the story.
- Poor connection in the spur or supply wiring Sometimes
A loose terminal at the fused spur or plug adds resistance that drops voltage exactly when the unit draws current. An electrician's fix, and worth finding — hot terminals are a hazard in themselves.
- Board power-section fault Rare
The measuring circuit can misread a healthy supply; diagnosed by measuring actual voltage at the appliance under load.
How to fix it
- Note whether other electrics dipped DIY safe
If the E34 coincided with dimming lights or tripped equipment, the supply itself dipped — likely a one-off. Reset once when things are stable.
- Reset once and observe DIY safe
Use the reset control (or switch off at the fused spur for 30 seconds and back on) a single time. If the code returns, stop resetting and book a Gas Safe registered engineer.
- Have a Gas Safe registered engineer complete the documented checks Gas Safe engineer
If it recurs, the engineer will measure the voltage at the appliance under load, distinguishing a supply problem (electrician territory — spur, wiring, or the network operator) from a board power-section fault (PCB replacement). Warm-air units are gas appliances, so the appliance-side work stays Gas Safe.
Parts you may need
- Control PCB · from £180
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 £90–£350, depending on the underlying cause.
Frequently asked questions
What does E34 mean on my Johnson & Starley?
The electrical supply reaching the unit dropped below the minimum the controls need, so it shut down to avoid running gas-safety components undervoltage. One-off dips clear with a reset; recurrence needs the voltage measured at the appliance to separate a wiring/supply problem from a board fault.
Is low voltage the boiler's fault or my house's?
Usually the house's or the network's — a loose spur terminal, tired wiring, or genuine brownouts. The appliance is the messenger. An engineer's voltage measurement under load points to the right trade: electrician for the supply side, Gas Safe engineer for the appliance.
Should I worry about a warm terminal at the spur?
Yes — a connection loose enough to drop voltage also generates heat, which is a fire risk in its own right. If the spur or its faceplate is warm to the touch, stop using it and have an electrician inspect it promptly.