Boat owners who take to the water even in cold weather have the best moorings all to themselves. Even though it can get particularly cold at night, the warm air from a diesel air heater ensures a cosy atmosphere below deck. This type of heater is usually very reliable, easy to operate and maintenance-free. Nevertheless, the system may occasionally fail, which is a nuisance as a technician is usually unable to come to your aid quickly.
We asked the heating manufacturer Webasto to explain what owners can sort out and repair themselves if necessary, should a breakdown occur unexpectedly.
Correct sizing
According to the expert, the main causes of problems are incorrect sizing of the heater and improper installation on board. A system that is oversized, for example, will always operate at the lower end of its power range – with the result that the burner wears out quickly.
It is therefore advisable to have the installation carried out by a professional, or at the very least to have it checked afterwards by a trained technician. This is because the heater’s proper functioning depends just as much on the correct length ratio of the combustion air and flue gas hoses as it does on an adequate supply of electricity and fuel.
Once this has been sorted out and the correct choices have been made regarding the cross-sections and lengths of cables and fuel lines, the warm air from the blower must be distributed on board via a hose. And this is where things get quite complicated: a specific value, corresponding to the air resistance, is assigned to every metre of hose, every branch, every bend and every outlet. If the system becomes too long and branched, nothing reaches the rear as the blower is overloaded. The result is a cold boat and a heating system that switches itself off due to overheating. DIY builders should therefore adhere strictly to the manufacturer’s specifications and also factor in potential sources of error. For example, the air hose running through the cupboard in the galley can be squashed if pots and pans slip out of place. A deflector is needed at such points, and even if it’s just a piece of guttering fixed over it, says the expert.
Disruption to operations
As well as installation faults, a common problem arises due to long periods of inactivity, usually over the summer months or after winter storage: the fuel has evaporated from the pipes, and when the heater is started, it takes a while for the feed pump to draw in diesel again. By this point, the burner has already attempted to ignite twice without success; the control unit stops operation and displays an error message on the control panel (in our case: ‘F 01’ – no start). If this process is repeated too often and no fuel has yet reached the burner, the control unit puts the heater into lock-out mode (“F 12” – heater lock-out).
A reset is then required; to do this, the power supply must be disconnected for five minutes (either directly at the battery or by unplugging the connector on the control unit). With older models, the fuel pump could simply be connected briefly to the battery to fill the lines with diesel, but the expert now strongly advises against this. Modern pumps operate at 8 volts and would be damaged immediately if this method were used. The only solution is to repeat the whole procedure until the heater starts up. Alternatively, as a preventative measure, you can run it regularly for a few minutes every now and then, even in summer.
If the heating is on but is making strange noises, smoking or giving off an unpleasant smell, there is something wrong with the combustion. In that case, you should check the points described; it may simply be that a fender is blocking the exhaust. If you can’t find the fault, it’s time to call in a technician.
What caused an air heater on board your vessel to break down on a previous occasion – and how did you identify the fault?
Michael Rinck
Redakteur Test & Technik