Off-peak / controlled-load contactor not switching
The contactor that switches a controlled-load (off-peak) supply — for hot water, slab heating, or pool gear — isn't operating in its window, so the load never gets power.
Safety first
Controlled-load involves a separate tariff supply and a switching contactor — isolate and prove dead. The tariff/meter side is the supply authority's.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Full detail — causes, the why, and common mistakes.
Likely causes
Ranked from most to least likely.
- 1
No control signal in the window (meter/tariff)
Most likelyThe contactor isn't being commanded because the controlled-load control signal isn't arriving in the tariff window.
- 2
Contactor coil / control fault
#2The contactor coil or its control wiring has failed (see contactor coil fault-finding).
- 3
Contactor contacts not making
#3The contactor energises but its contacts don't pass the load.
- 4
Wiring fault on the controlled-load supply
Least likelyA fault in the dedicated supply wiring.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
During the tariff window, check whether the contactor is being commanded (coil energised).
Coil energised in the window.
Commanded — check it pulls in and its contacts pass the load.
No command — the control signal/meter side isn't switching (authority).
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Off-peak contactor not switching
→ step 2 - 2decision
In the window, is the contactor commanded (coil energised)?
Yes→ step 3No→ step 4 - 3decision
Does it pull in and pass supply to the load?
Yes→ step 5No→ step 6 - 4result
No command — tariff/meter side (supply authority).
- 5result
Load supplied — re-check downstream (element/load).
- 6result
Coil/contacts fault — rectify (see contactor faults).
Common mistakes apprentices make
- Testing outside the tariff window.
- Assuming the load when the contactor isn't commanded.
- Overlooking non-making contacts on an energised contactor.
- Confusing the tariff/meter side (authority) with the contactor.
When to stop & escalate
Contactor/wiring work is licensed; the controlled-load tariff/meter switching is the supply authority's. Coordinate accordingly.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
Related faults
Off-peak / controlled-load hot water not heating
A controlled-load (off-peak) hot water system isn't being energised during its tariff window — the element and thermostat may be fine, but power never arrives at the right time.
Contactor has voltage at the coil but won't pull in
You measure the rated control voltage (e.g. 24V) across the coil terminals, but the contactor refuses to energise — no clunk, no pull-in, contacts stay open.
Contactor contacts welded closed — load won't switch off
The contactor won't drop out when the coil is de-energised. The load stays powered even with the control circuit off, because the main contacts have welded together.