Posted: Fri Aug 13, 2010 7:35pm

My son has just purchased a narrow boat which has a Eberspacher heater and a coal stove, with the Eberspacher on the 3 radiators got hot except for two, one which was hot only at the bottom and the one in the bathroom (other side of the boat)which was cold. We bled the system of air and filled the expansion bottle with plain water, as the water got hot it just came out of the expanion bottle,and now it does not get hot at all , as I had left the boat I suspect that he did not have the central pump running and noew the expanion bottle is empty. I felt that the radiator cap was faulty and said to replace that as no pressure was built up at all. How does the system ger rid of excess heat if you just want the coal fire on or do you have to run radiators as well, is there anywhere I can find a diagram of how these systems work. Hope this makes sense Thanks for any replies.

Posted: Sat Aug 14, 2010 8:08am

Dear Ray, The Eberspacher should have its own circulating pump so it is impossible to run it without the pump working. If we assume a pumped system for a moment then the usual cause of radiators not getting hot when the pipes do once an airlock is ruled out is that someone has filled the system without pre-mixing the antifreeze and water. Your topping up with ordinary water will not help. Hot antifreeze is denser than water so with some systems the hot antifreeze will not rise up into radiators even though the pipes are hot. This should not happen on a pumped system as readily so I wonder if the valves on the radiators have not been properly set to balance the system. Also once the water was up to temperature the Eberspacher should have shut down or gone into low output mode so there should be no way to empty the header tank. Normally that happens when water in the system boils so steam displaces water. If you overfilled the bottle water would come out as heat was applied causing the water to expand but unless the expansion tank is undersized it should not have emptied it. The radiator cap should not be necessary and may be positively dangerous if it is used to pressurise the system with the stove in use. Both the Eberspacher and stove should work with an open vented system. Unfortunately with so may different boat builders and DIY fit out around it is impossible to give definite advice without inspecting the boat. It is possible that there is a second central heating pump that is used when the stove is alight and this may have still been turned off. The stove part of the system could circulate by gravity (if so it should have very large pipes running down the boat) but I doubt the radiator in the bathroom would work very well on a gravity system and they are very intolerant of unmixed antifreeze. The symptoms you give sound much more like a stove with a back boiler being lit without a circulating pump running because, as I said, the Eberspacher should shut down when it reaches temperature. If the stove has a back boiler the answer to your question about wanting the stove alight without the radiators working is simple - you do not. You MUST have the pump running and the one or two radiators turned on to dump the heat from the boiler and prevent boiling and a possible explosion. If you want diagrams of how the system works you first need to find out exactly how the boat has been plumbed and draw it out making sure you show all the valves etc. Then I am afraid it is a visit to your library to search the DIY & professional central heating books to find a system similar to yours. I expect it will turn out to be a mixture of two systems. If it did not come with the boat I would suggest you go to http://www.eberspacher.com/support-and-downloads /technical-documents.html and try to find the operating manual and installation instructions for the heater. Tony Brooks

Posted: Sat Aug 14, 2010 5:56pm

Thanks Tony now pretty sure central heating circulating pump was not turned on, lets hope it has not done any damage, will refill system to test with plain water and if all ok drain out and refill with 50/50 antifreez. He now has problems with the alternator on the lesuire batteries on which I have posted a question. Oh tje fun of an unknown boat.