Blowing cold air
Different fault, similar symptom. The fan keeps running but no warm air.
Help guide · Short cycling
Heater fires up, then shuts off? Usually an easy fix.
The technical name is "short cycling" — and 7 times out of 10 in Adelaide it's a flame sensor that's collected a bit of carbon and lost its ability to confirm the burner is alight. The safety system does what it should and shuts the gas off. Quick clean, you're back in business. Here's how to know if that's your fault — and what else it could be.
Same-day metro Adelaide
Most fixes under $300
Upfront pricing
Licensed gas fitter
45–75 min on site
Often under $200
CO test included
What's happening
The flame sensor is missing the flame
Every modern gas heater has a small probe sitting in the burner flame called a flame sensor (or flame rectification rod). When the burner is lit, the flame conducts a tiny electrical current from the rod to ground. The control board sees that current and goes "yep, the flame is real, keep the gas on". When the current drops, the board can't be sure the gas is being burnt — so it shuts the valve straight away. That's the cycle you're hearing.
The current is tiny — measured in microamps. Anything that interrupts the path will trip the safety: a thin layer of carbon on the rod (extremely common after a season of dust and combustion), a slightly bent rod no longer touching the flame properly, or — less commonly — a failing control board.
Other causes that look identical from the outside: overheating because the filter is blocked, a thermostat with bad contacts that keeps cutting the call for heat, or low gas pressure starving the burner mid-cycle. We work through all of them.
Safety check
Is this dangerous?
Mostly no. The shut-off is the safety system doing its job. Each cycle stops cleanly with no gas escaping into the room. CO risk is low because the burner is off most of the time.
What's not ideal: repeated ignition cycles wear out the igniter and gas valve much faster than normal use. A heater short-cycling 50 times a night is doing a year's worth of wear in a week. Fix it sooner rather than later — what's a $140 flame sensor clean today becomes a $400 gas valve in two months.
Stop and call us if: you can smell gas at any point, the heater bangs on ignition (see banging on ignition), or the flame looks yellow or lazy when it does light.
Right now
What to do in the next 5 minutes
1
Time a cycle
How long does it run before cutting? Under 2 minutes is short-cycling. 15–25 minutes is normal thermostat behaviour.
2
Check the filter
Ducted system: pull the return-air filter, check it's not choked. Wall heater: check the back/sides for dust build-up.
3
Check the thermostat
Set well above current room temp. If batteries are old, replace them. Wiggle a wall thermostat — bad contacts show themselves.
Diagnosis
What's likely causing it
- Dirty flame sensor (about 60% of cases). Carbon coats the rod and breaks the flame-detection signal. Quick clean with abrasive paper, re-test, done. $45–$140.
- Overheat lockout from blocked filter. Blocked filter starves the fan, heat exchanger temperature climbs, the safety switch shuts the burner off until it cools. Replace filter — $80, or free as part of a service.
- Thermostat fault. Failing contacts in an old wall thermostat or low batteries in a wireless one cause it to drop the call for heat intermittently. Replace thermostat — $180–$320.
- Low gas pressure. Burner starts on low pressure, doesn't establish a strong flame, sensor drops out, valve shuts. Pressure-tested with a manometer on every callout.
- Failing gas valve. The solenoid is weak and won't hold the valve open under load. $400–$650 fitted, less common.
DIY?
Can I fix it myself?
You can do three safe things:
- Replace or clean the return-air filter on a ducted system. Vacuum any dust from around a wall heater's air intakes.
- Replace thermostat batteries if it's wireless.
- Cycle the unit at the isolator switch — off for 30 seconds, then on. One reset attempt.
Beyond that, every part of the gas system — including cleaning the flame sensor — has to be done by a licensed gas fitter under SA's Plumbing, Gas and Electrical Services Act 1995. Even removing the burner cover voids your insurance.
When to call
Call us today if
- The heater is firing for under 2 minutes per cycle
- Filter, thermostat batteries and reset didn't fix it
- The cycle frequency is getting worse, not better
- You hear a click or whoosh on shut-off (igniter or gas valve symptoms)
- The system hasn't been serviced in 2+ years
Honest pricing
How much will the repair cost?
2026 Adelaide pricing, GST included, no call-out fee:
- Flame sensor clean: $45–$140 (depending on access)
- Filter replacement: $80
- Diagnostic + minor adjustment: $180
- Thermostat replacement: $260–$420
- Igniter replacement: $260–$330
- Gas valve replacement: $400–$650
- Full service + flame sensor clean: $209 — clears the underlying carbon and resets the heater
If we can't fix it in one visit because we need a brand-specific part, we'll quote the cost upfront and order it the same day.
Response time
How quickly can you come out?
Same day across Adelaide metro if you ring before 10am. Most short-cycling jobs take 45–75 minutes on site — diagnose, clean or replace the part, pressure-test, CO check, done. After-hours callout is $249 if it's making your house unliveable in the cold.
FAQ
Heater keeps shutting off — common questions
Most common is a dirty flame sensor — the probe loses its ability to detect the flame so the safety shuts gas after 30–60 seconds. Other causes: blocked filter overheat, thermostat fault, low gas pressure, failing gas valve.
Heater fires up, runs briefly, shuts off, repeats. Healthy heaters run for several minutes per cycle. Under 2 minutes per cycle is short-cycling and needs a fitter.
The shut-off itself is the safety system working. But repeated cycling wears ignition parts fast and the underlying cause may be more serious. Book a fitter.
Flame sensor clean $45–$140. Filter $80. Thermostat $180–$320. Gas valve $400–$650. Most callouts resolved in the first visit for under $300.
Same-day Adelaide metro if you ring before 10am. Most short-cycling jobs are 45–75 minutes on site.
Related help
Other gas heater problems we help with
Error code on the controller
Brand-specific codes decoded — Braemar, Brivis, Bonaire, more.
Annual service from $149
A yearly service prevents most short-cycling faults from happening at all.
Heater short-cycling? Book today — usually a same-visit fix.
Same-day Adelaide metro. Most jobs under $300. Upfront pricing, no surprises.