Zone valve not opening
Checks for an indirect cylinder when the zone valve won't open.
Use this guide for an indirect cylinder when the boiler or heat pump isn't heating the cylinder.
SAFETY
Only carry out electrical or unvented hot water checks if you are competent to do so. Isolate the supply and prove it dead before you remove covers or touch wiring, and never ask a homeowner or resident to access live components.
Follow these checks in order
1. Confirm the cylinder is calling for heat
- If not, make sure a schedule or a manual Boost is calling for heat.
- If yes, go to step 2.
2. Check power to the zone valve
When the cylinder is calling for heat, there should be 230V AC on the brown wire.
- If there's no voltage, check the controller output and the wiring.
- If there is, go to step 3.
3. Check the valve motor
Feel for movement or slight vibration when it's energised, and listen for the typical hum or click. Is the valve powered but not moving?
- If yes, the valve motor has failed or the valve body has seized, and it needs replacing.
- If not, go to step 4.
4. Check the end switch (microswitch)
Test continuity across the grey and orange wires, with 230V AC at both connections. When the valve opens, does the switch close?
- If not, the microswitch is faulty. Replace the zone valve actuator.
- If yes, it isn't a Mixergy fault. Check the indirect heat source.