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.
Safety first
Isolate before working at the system. Controlled-load wiring involves a separate tariff supply/contactor — confirm what's live before working.
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.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
Off-peak contactor / relay not closing
Most likelyThe contactor that switches the controlled-load supply isn't closing during the tariff window.
- 2
Tariff signal / meter timing issue
#2The controlled-load isn't being switched on by the meter/tariff control (supply-authority side).
- 3
Wiring fault on the controlled-load supply
#3A fault in the dedicated off-peak supply wiring.
- 4
Element/thermostat fault (coincidental)
Least likelyThe element or thermostat has also failed — confirm separately.
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.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModeDuring the expected heating window, check whether the controlled-load supply is actually energising the element.
Controlled-load supply present at the system in its window.
Power arrives — the fault is the element/thermostat (see no-hot-water).
No power in the window — check the off-peak contactor and tariff control.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Off-peak not heating
→ step 2 - 2decision
In the window, is the controlled-load supply reaching the element?
Yes→ step 3No→ step 4 - 3result
Power arrives — fault is the element/thermostat.
- 4decision
Does the off-peak contactor close and is the wiring sound?
Yes→ step 5No→ step 6 - 5result
No supply upstream of a closing contactor — tariff/meter issue (authority).
- 6result
Contactor not closing / wiring fault — rectify.
Common mistakes apprentices make
- Replacing the element when the controlled-load never energises.
- Not testing within the actual tariff window.
- Overlooking the off-peak contactor.
- Assuming a property fault when it's a meter/tariff control issue.
When to stop & escalate
Controlled-load wiring/contactor work is licensed electrical work; tariff/meter switching is the supply authority's domain. 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.
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Related faults
No hot water (electric storage system)
An electric storage hot water system has gone cold — no hot water at the taps. Usually the element, thermostat, supply, or (for off-peak) the tariff/timing.
Hot water runs out too quickly / not hot enough
There's some hot water but it runs out fast or never gets properly hot — often a partially-failed element, a thermostat set low, or a system being asked to do more than its size.
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.