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No hot water

Work through these checks in order to find out why a Mixergy cylinder isn't giving hot water.

Start here when there's no hot water at all and you don't yet know why. Work through the checks in order.

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. Check there's power to the cylinder

Is the gauge lit, is the fused spur switched on and is the circuit breaker not tripped?

  • If there's no power, restore it and confirm the cylinder comes back online.
  • If the circuit breaker has tripped and won't reset, don't keep resetting it. An electrician or engineer needs to investigate.
  • If there is power, go to step 2.

2. Check the cylinder isn't switched off at the gauge

A single red light on its own means the cylinder has been switched off at the gauge.

  • If so, press the power button on the gauge and confirm it starts heating.
  • If not, go to step 3.

3. Check whether the cylinder is already charged

Does the app or portal show the cylinder charged (for example 60 to 70°C at the top) while the taps still run cold?

  • If yes, the cylinder is working. Suspect a fault elsewhere in the system, such as a blending valve, an isolation valve or the supply, and check the plumbing.
  • If no, go to step 4.

4. Check which heat source the cylinder is set to use

Look in the app to see whether the cylinder is set to heat directly (electric immersion) or indirectly (boiler or heat pump).

  • For direct (electric) heating, go to step 5.
  • For indirect heating, go to step 7.

5. Check whether the immersion thermostat has tripped

Isolate the power, then reset the thermostat.

  • Black thermostat: press the black button.
  • Grey thermostat: press a pin into the black circle.
  • Solar X: with the power off, press the red button or buttons on the underside of the diverter firmly, then power back on.

Did the reset restore heating?

  • If yes, it's resolved. Ask the customer to get in touch if it trips again.
  • If it worked only briefly, go to step 6.
  • If you found no trip and it still won't heat on electric, check the top-up pump and the immersion. See Charge stuck at 10 to 30% and Test an immersion heater.

6. Check whether it trips again

Does the thermostat trip again, either straight away or within days?

7. Check the boiler or heat pump

Is the boiler or heat pump itself running and reaching temperature?

  • If not, it's a heat source fault for a boiler or heat pump engineer, not a Mixergy fault. If an immersion is fitted, switch the heat source to electric in the app to restore hot water in the meantime.
  • If yes, go to step 8.

8. Check the boiler flow temperature

Is the boiler flow set at least 10°C above the Mixergy target temperature?

  • If not, raise the boiler set point (for example, a Mixergy target of 50°C needs a boiler flow of 60°C). Recheck after the next heat.
  • If yes, go to step 9.

9. Check the zone valve opens on a call for heat

Is there power at the brown cable, and does the valve move?

  • If not, the zone valve may be stuck or dead, or the indirect common may be wired to a timer feed instead of a permanent live. Correct the wiring, or replace the valve if it's confirmed faulty. See Zone valve not opening.
  • If yes, the wiring, controls or data need investigating. Contact Mixergy support with the MX number for a remote data check.