Webasto Water Heater, running on empty water tank ?

[seumask]

We have a Webasto water heater (approx. 4 years old) and a wet heating system in the form of a blown air heat exchanger on our boat. During the winter when the boat is laid up ashore I drain down the water tank and calorifier that is connected to the webasto for heating the water. I would like to heat the boat when I am aboard doing jobs but I am not sure whether it is sensible to run the webasto to warm the boat up without ensuring the calorifier is full of water! Can anyone comment on whether this system can be run without the calorifier being full and if there are any other sensible things I need to look out for. Your comments greatly appreciated.

 

[pvb]

Running hot water through the calorifier coil of an empty calorifier won't damage it.

 

[seumask]

My main concern is the cycling on and off of the webasto, without the mass of water to heat up it is really just the air blown radiator and the small amount of water in the pipes and I could see that this may cycle the webasto on and off rather a lot. My understanding is that on the whole these heaters should be driven for longer periods of time or they can coke up! or is this not really an issue. Again thanks for any comments.

 

[rob2]

Just an observation, I think you could be right and might expect to coke up, long-term, as the heater will not get hot enough for long enough to burn all the deposits. Some support for this is suggested by the inclusion in all example Eber circuits of a radiator/towel rail, presumably to load the circuit more than a blower will.

Rob.

 

[pvb]

My main concern is the cycling on and off of the webasto, without the mass of water to heat up it is really just the air blown radiator and the small amount of water in the pipes and I could see that this may cycle the webasto on and off rather a lot.

You don't say which Webasto heater you have, but they usually automatically drop down to a partial load setting when the water reaches a certain temperature. The partial load setting is typically only about 2kW, and I'd have thought you'd have been using that much heat via the matrix heater, so the Webasto shouldn't switch on and off.