Brivis fault code h01 40
Return-air overheat, flue-fan overheat switch open.
What h01 40 actually means
The heater has shut down because the air coming back to it is too hot, or the flue fan's overheat switch has opened. Nine times out of ten the heater is fine and it simply cannot get enough air through itself, so heat builds up inside the cabinet and the safety switch does its job.
What causes it
- A blocked or filthy return-air filter, by far the most common cause and the one you can fix yourself
- Furniture, a rug or a piece of board sitting over the return-air grille
- Too many ceiling vents closed, so the heater has nowhere to push air
- A failing main fan that is turning too slowly to move the heat away
- A blocked or partly collapsed flue
Most likely first. That order is from what we actually find on site, not from the manual.
Safe to check yourself
No tools, no covers off, nothing to do with gas, refrigerant or wiring.
- Pull the return-air filter out and look at it against the light. If you cannot see through it, that is your fault code
- Check nothing is sitting on or against the return-air grille
- Open every ceiling vent in the house, including the ones in rooms you do not use
- Turn the heater off at the controller for ten minutes, then restart it
What we check on site
So you know what you’re paying for.
- Measure the temperature rise across the heat exchanger against the data plate
- Check main fan speed and current draw
- Inspect the flue and the flue fan for blockage or bird nesting
- Test the overheat switch and the supply-air thermistor
- Check the ductwork for crushed or disconnected runs in the roof
Can you keep using it?
It will usually restart itself once it cools down, and it is safe to let it. But if it keeps tripping, stop using it and book someone. Repeated overheating is what cracks a heat exchanger, and a cracked heat exchanger is a carbon monoxide problem rather than a heating one.
What the fix usually involves
Most of these are a filter and a duct check, done in one visit. Where the fan or the overheat switch has genuinely failed it is a parts replacement, and Rinnai stock Brivis parts in Melbourne for units well over a decade old.
Is it worth fixing?
That depends almost entirely on how old the unit is. Past about ten years on hot water and gas heating, and twelve on aircon, a significant repair usually costs more per remaining year than a replacement does — and it’s the same point at which the VEU rebate is worth the most, because old inefficient appliances are exactly what the scheme pays to remove. If yours is young and the fault is a component, we’ll fix it and say so.
Repair or replace? The 10-year rule, and what the rebate is worth →