Error S.30

Safety first

- If you smell gas, leave the property immediately and call the gas emergency number. Do not try to fix the boiler.

- Turn off electricity to the boiler at the isolator before touching wiring or opening any electrical boxes. If you are not competent with electricity, do not open electrical panels or attempt wiring changes. Call a qualified person.

- Do not dismantle the boiler casing or attempt internal boiler repairs unless you are a Gas Safe registered engineer.

Initial homeowner checks (easy, no tools or simple tools)

1) Check the programmer/timer: Ensure the heating programme is set to ON or is in a timed ON period for CH (central heating). Sometimes the timer is set to HW only or to OFF.

2) Check the room thermostat: Raise the thermostat temperature well above current room temperature or switch it to a manual/override HEAT position. If it is a digital/wireless stat, try switching to 'on' or 'call for heat'.

3) Batteries: If the thermostat or its wireless handset uses batteries, replace them with fresh batteries. Wireless stats commonly stop calling for heat when batteries are low.

4) Boiler mode: Ensure the boiler is set to allow heating (not just DHW/hot water). Use the boiler controls to confirm CH mode is available.

5) Power reset: Switch the boiler off at the mains or isolation switch, wait 30 seconds, then switch back on. Some intermittent faults clear with a reset.

If those checks do not restore heating, proceed to more specific diagnostics

6) Check the wireless receiver or thermostat relay box: If you have a wireless stat, find the receiver (often near the boiler or in an airing cupboard). Many receivers have an override or test button which will force a call for heat — press this while watching the boiler to see if it fires. If the receiver shows no power or lights, it may be unpowered or faulty.

7) Listen and watch the valve/pump: Turn heating on and listen for the pump or hear the motorised valve move. If the hot water demand fires the boiler but heating does not, the issue is likely in the heating control path (room stat, programmer, 3‑port or zone valve, or zone relay boxes).

8) Motorised valve check (if you have one): Many systems have a 3‑port valve with a plastic lever on the valve head. If safe and accessible, move the lever manually to the heating position and see if the boiler and pump start. If the boiler fires when you move the lever, the valve actuator or its microswitch may be faulty.

9) Zone/relay boxes and multiple stats: If you have multiple thermostats and relay boxes (multiple zones), check that each relay has power and that any green LEDs indicate a call when the stat is turned up. A failed relay or wiring fault in a zone can stop the boiler from receiving a call.

10) Wiring / connections: For a simple wired room thermostat there are usually two thermostat wires that form a switch. If you are competent and the boiler is isolated at the mains, you can temporarily link (bridge) the two thermostat wires at the thermostat terminal or at the boiler’s control terminals to see if the boiler fires. Only do this if you are experienced with basic electrical safety. If bridging makes the boiler fire, the thermostat or its wiring is the likely fault.

When you should call a professional

- Call a Gas Safe registered heating engineer if: you are not comfortable doing the checks above; bridging or receiver override is needed and you don’t know how to proceed safely; the problem is intermittent; the motorised valve, zone valve, receiver or boiler wiring looks faulty; the boiler shows other error codes; or any internal boiler work is required.

- Call an electrician if you suspect a wiring fault to the thermostat or receiver and you are not qualified to test/repair it.

Extra notes and common causes to tell the engineer

- Common homeowner fixes: batteries in wireless thermostat, timer set to off, thermostat set too low, receiver in OFF or showing no power.

- Common engineer fixes: replace wireless receiver, replace faulty room thermostat, repair/replace motorised 3‑port valve or actuator, repair failed zone relay or wiring.

- Intermittent S.30 after several hours can indicate a failing room thermostat, failing valve microswitch, or receiver going into a fault state; these often need professional diagnosis.

If all else fails and you still have S.30 displayed, stop attempting further electrical work and arrange for a qualified Gas Safe engineer to diagnose and repair the control/valve/receiver or any wiring faults. The code itself is not usually a gas-safety emergency but the underlying cause may require professional attention.