Just to confirm the comment above, we have been on a canal boat for the last couple of weeks and it was fitted with an Eberspacher heater. It heated the 45 foot boat in minutes and started as soon as we finished a day's cruise with no problems. However, in the morning, we could not get it to start without running the engine first. Once it was going, we could switch the engine off and it carried on fine, but without the engine running, it would not ignite and keep burning. The engineers seemed to accept this as the norm.