Truma Combi Heater Not Working: Common Faults and the Parts That Fix Them

Truma Combi Fault Finding

A practical guide from Bedam Leisure — caravan & motorhome specialists

When a Truma Combi heater is not working, the cause is almost always one of five things: no gas, no 12V, a blown fuse, a blocked or damaged roof or wall cowl, or a failed fan motor. Work through them in that order and you will identify the fault on most vans in twenty minutes, without taking a single panel off.

The Combi is a reliable unit, but it is a gas appliance with a 12V brain, a 230V element and two fans, so there are several very different reasons it can sit there doing nothing. Helpfully, it tells you a lot by how it fails: completely dead is a different problem from whirr-click-lockout, which is different again from one that runs happily on gas but refuses to heat on electric. This guide walks the fault tree the way the trade does, from the symptom you can see to the part that usually fixes it — all of it in our Truma Combi 4 and Combi 6 spares range.

1 Start here

The five checks before you spend anything

Most "the Combi has packed up" calls end at one of these, and all five are free.

1. Gas. Cylinder not empty, cylinder valve open, heater manifold valve open. A bottle that feels heavy can still be useless in cold weather — butane stops vaporising properly around 2°C, exactly when you want the heater.
2. 12V. The Combi will not light on gas without it — ignition, board and fans all run on 12V. A flat leisure battery is the commonest cause of a dead heater in spring.
3. The fuse. A blown fuse on the heater's own board kills it completely while the rest of the van works normally.
4. The cowl. Go outside and look. A nest, leaf pack, snow drift or winter cover over the flue stops the heater within a minute of lighting.
5. Mode and settings. Not in a water-only mode, room temperature set above cabin temperature, no timer or app override.

Coming out of storage? Do the 12V check properly — measure the battery, don't judge it by the panel lighting up. More on keeping it healthy in our winterising guide.

2 Dead

Completely dead: no panel, no fan, no click

A blank panel and no response means the heater has no 12V — either the van has none, or something between the van and the heater is stopping it getting there.

Start at the battery: a resting 12V leisure battery should read 12.7V or more, and below about 11V most control electronics refuse to play even though lights and pumps still work. Charge it properly and retest before condemning anything on the heater. If the supply is good, the next suspect is the board fuse — a small glass cartridge, under a tenner, that produces exactly this symptom. Replace it with the correct Truma rating; if the new one goes straight away, stop and get the heater looked at, because something downstream is drawing current it should not.

Before you order anything: unplug and firmly reseat the panel cable at both ends. Pins back out of their housings over years of vibration, and a reseated plug has fixed more "dead" Combis than any part we sell.

3 Lockout

It tries to light, then locks out

This is the classic Combi fault, and the one people most often describe as "the Truma Combi is not igniting". You turn it on, the fan spins up, the igniter ticks, and after fifteen or twenty seconds it gives up and shows a fault — sometimes three times over before locking out properly. The heater is telling you it never got a flame, or got one and lost it. Three things cause that, in this order of likelihood.

Gas supply

Not just "is there gas" but "is there gas at the right pressure". An aged regulator, a hose past its date or a nearly-empty cold cylinder all deliver gas too weakly for the burner to establish. A hob lighting normally proves nothing — it needs far less. Swapping to a known-full cylinder is the quickest test there is, and a regulator over about ten years old, or with no date on it, should be replaced: see our gas safety guide, or the standard UK Truma 30mbar regulator (52400-01).

A blocked or damaged cowl

The Combi draws combustion air in and pushes exhaust out through one cowl. Block it and the heater cannot breathe, so it lights and shuts straight down. Wasps, birds and spiders love a warm flue, and so does a winter cover fitted over the top of one. Outer mouldings also go brittle with UV, and a split one lets exhaust back into the air intake — same intermittent lockout.

The combustion air fan

With the cowl clear and the gas good, the next part is the combustion air motor. The board monitors it, so a motor with dried-out bearings is shut down before the heater ever lights — the short whirr-and-stop owners describe as the heater "trying". A workshop job on most installations, but a repair rather than a new heater.

Reset it properly. Switch the heater fully off at the panel, wait a few minutes, switch it on again — a quick off-and-on often will not clear the fault. If it locks out three times in a row, stop resetting and find the cause.

4 Electric side

Gas works, electric doesn't

A Combi E makes heat two completely separate ways: the gas burner, and one or two 230V immersion elements. They share a water vessel and a control panel and nothing else, so one failing while the other works perfectly is entirely normal.

Check the simple things first — actually on hook-up, RCD and 230V breaker in, enough amps at the bollard. On a 6A pitch, full electric output plus a kettle trips the supply every time, and plenty of owners read that as a heater fault. If the supply is sound it is either the 230V board or the element: an element failed open circuit simply does nothing, while one failed to earth trips the RCD the moment you select electric.

5 No heat

It runs, but the van never warms up

The heater lights, stays lit, shows no fault and still leaves you cold. Nine times in ten that is air, not fire. The Combi blows warm air through ducting to outlets around the floor, so a failed circulation fan means heat with nothing to move it — warmth at the unit, nothing at the vents. Crushed, kinked or disconnected ducting behind a locker does the same locally, and is worth a torch and five minutes before you order a motor.

The other common cause is the room temperature sensor: if it reads high the heater satisfies itself almost immediately, cycles briefly and never gets the van there. A sensor in the wrong place — above a 12V socket, in sunlight, behind a cushion — does the same, so check where yours is first.

6 The panel

The control panel, the board, and error codes

A cp+ panel that is blank, frozen or flickering is not necessarily a sick heater. The panel, its cable and its knob are replaceable on their own and far cheaper than the boards behind them — a knob that no longer clicks cleanly through its detents is a worn encoder, not a control fault. Behind it sits the main 12V board, the part to suspect when the panel is alive but the heater ignores it entirely, with fuse and supply both proved good. Boards are model and generation specific, so match on part number, not on the shape of the heater.

Got a Combi 2E? Different board — the Combi 2E PCB cp+ (34030-26400). Check the rating plate before ordering any board, and send us the part number if you are not sure.

What the error code is telling you

Write the code down before you clear it — it narrows the search enormously and it is the first thing any engineer asks for. Codes are listed in the instructions for your specific Combi and are not interchangeable between models, so look yours up rather than trusting a forum post about a different heater. As a rule, warnings are supply problems the heater clears itself once conditions improve, low voltage by far the most common, while hard errors needing a manual reset point at ignition, exhaust or fan faults. A heater warning about low voltage every evening does not need a board; it needs a better battery or one of our battery chargers.

Common questions

Why is my Truma Combi not igniting?

Nearly always gas supply, 12V supply or a blocked cowl. The heater needs 12V for its ignition and fans even on gas, so a tired leisure battery stops it lighting. Try a known-full cylinder, charge the battery and check the cowl before suspecting the heater.

Why does my Combi work on gas but not on electric?

The burner and the 230V element are independent, so one failing does not affect the other. Check you are on hook-up, RCD and breaker in, with enough amps at the pitch. If that is fine it is usually the 230V board or the element — an element failing to earth trips the RCD the instant you select electric.

My heater runs but the van stays cold. What is wrong?

Almost always the air circulation fan or the ducting rather than the heater. Hold a hand over the floor vents: no airflow points at the fan motor or a duct off its spigot, airflow with short cycling points at the room sensor.

Can I fit Truma Combi parts myself?

Fuses, cowl mouldings, control knobs, panel cables, duct clips and room sensors are reasonable owner jobs. Anything inside the heater, or touching the burner, gas valve or pipework, needs a Gas Safe registered engineer with LPG and caravan or motorhome qualifications.

How do I know which board or part fits my heater?

Go by the rating plate on the heater, not the model of the van. Combi 2E, 4, 4E and 6E parts differ, and boards changed generation around 2018 with the move to cp+ and iNet control. Send us the part number from the plate and we will match it.