With win­ter just around the cor­ner it’s time to do a few checks on your boat’s heat­ing and think about a lit­tle main­te­nance to keep things warm

Canal Boat - - Contents - WORDS BY CANAL BOAT

How to main­tain your boat’s heat­ing


First things first, check the ex­haust – is it still in one piece? Flex­i­ble ex­haust sys­tems can get brit­tle over time and, if knocked or dis­turbed dur­ing sum­mer cruis­ing or main­te­nance, can leak, which isn’t a healthy ex­pe­ri­ence. Make sure too, es­pe­cially if the boat is new to you, that no one has fit­ted a ve­hi­cle ex­haust si­lencer. Ve­hi­cle ex­haust si­lencers aren’t gas tight or in­su­lated and should def­i­nitely not be fit­ted in a boat. Also check the heater’s fuel sys­tem for leaks or cor­ro­sion and en­sure the com­bus­tion air pipe hasn’t been crushed.


Just like a car, the coolant isn’t just there to stop things freez­ing up and, as with a car, if you ne­glect the an­tifreeze the cor­ro­sion in­hibitors be­gin to de­grade or get used up. If this hap­pens the ra­di­a­tors be­gin to rust in­ter­nally and the en­tire sys­tem starts to sludgeup. As the rust con­tent builds it can also cre­ate elec­trol­y­sis in the heater caus­ing it to eat it­self from within. An­tifreeze also lu­bri­cates the water pump in some heaters and will stop limescale build-up around crit­i­cal parts.

If you are us­ing a long-life coolant, the heat­ing sys­tem should be drained down, flushed out, and fresh an­tifreeze water/ mix added ev­ery five or six years; two to three years for stan­dard an­tifreeze. Add one or two years if you use de-ion­ized water. Eberspächer rec­om­mend a 50/50 mix of any stan­dard Gly­col based ve­hi­cle an­tifreeze and water, other man­u­fac­tur­ers may dif­fer, but never use more than a 50/50 mix or house­hold in­hibitors.

Here’s a tip: never add neat an­tifreeze into a sin­gle pipe header tank, it will just sit there in the tank fool­ing you into think­ing your coolant sys­tem looks great...


If your boat has had lit­tle use over the sum­mer, think about your fuel qual­ity.

Is it old? Is there any sign of diesel bug? Also, head­ing into a harsh win­ter with a tank full of sum­mer diesel can be a ba­sic er­ror. Fuel sup­pli­ers should switch from sum­mer diesel to win­ter diesel dur­ing Septem­ber.

Sum­mer diesel should start ‘wax­ing’ from -5°C, but de­pend­ing on FAME con­tent, water, age etc. this num­ber can de­te­ri­o­rate. So, as you get to the point when you re­ally need your heater, it may fail due to fuel star­va­tion caused by the fuel ‘wax­ing’ and by the time the en­gi­neer turns up, the tem­per­a­ture has risen so the heater starts first time.


If the heater hasn’t been started for a few months, it might not want to start first time. This is not gen­er­ally the heater’s fault; it’s nor­mally caused by dead fuel in the cop­per fuel line. Cop­per de­grades diesel at an alarm­ing rate and when cop­per fuel line is used, it gen­er­ally has an ex­tremely small bore size (usu­ally 2mm in­ter­nal di­am­e­ter) for most heaters.

This equates to a minute amount of diesel com­pletely sur­rounded by cop­per, so within a few months, the cop­per will have ox­i­dised and de­graded the diesel to the point it will no longer ig­nite with­out com­pres­sion. After two or three start at­tempts, the heater will have pulled the fresh diesel from the tank and you’ll be greeted by a brief cloud of smoke as the un-burned old diesel is burnt off. This is a good time to check for ex­haust leaks.

As soon as the heater starts, check the fuel sys­tem again for leaks.


Once the heater has cleared any old diesel from its fuel lines, it should start cleanly with­out ex­ces­sive smoke. The sound em­a­nat­ing from the ex­haust should be clear, crisp and even, a steady roar or, if you have a fully si­lenced marine ex­haust, a steady whis­per. With the boards up, lis­ten to the in­take noise. This should be a steady whine, if no com­bus­tion air pipe has been fit­ted the whine will be quite loud but it should be steady, if you hear the whine chang­ing er­rat­i­cally it can be a good in­di­ca­tion that the blower mo­tor will not last till spring. If your heater goes out when try­ing to start from cold, puff­ing a big cloud of white smoke across the ma­rina, this can be a sign the flame tube is get­ting to the end of its life.

There are many lit­tle things you can do to make your heater last much longer and work more ef­fi­ciently and most diesel heaters work in a sim­i­lar way.

En­sure your heater has a com­bus­tion air pipe fit­ted and en­sure it’s tak­ing cool air from the en­gine air vent at least. If you go out­side the en­gine bay with a skin fit­ting, push the com­bus­tion air hose into the skin fit­ting so as not to re­strict it in any way.

Why? The max­i­mum al­low­able com­bus­tion air tem­per­a­ture for a 4kW or 5kW water heater is 25°C. This is be­cause the air is used to cool the two most ex­pen­sive parts of the heater, the ECU (brain) and blower mo­tor. If you use 75°C air from the en­gine room it will cause pre­ma­ture fail­ure of these parts. If no com­bus­tion air pipe is fit­ted, you will be pulling 250°C air straight from the ex­haust spigot! Bear in mind your en­gine room will re­main hot for hours after the en­gine has been run­ning.

Bal­ance the water sys­tem prop­erly. A diesel heater con­stantly switch­ing on and off (short-cy­cling) will rapidly drain a large bank of bat­ter­ies and might ul­ti­mately coke-up and fail. Plumb­ing is a cu­ri­ous thing; it should be sim­ple, but it ac­tu­ally ac­counts for more heater is­sues than any­thing else. If you sort the plumb­ing out your heater will run more ef­fi­ciently, re­li­ably and your boat will warm-up faster with a more even heat spread.


One of the best pre­ven­ta­tive mea­sures you can do is to run your heater once a month, if pos­si­ble. Just 15 to 20 min­utes will keep the fuel fresh in the fuel lines, stop solid se­da­tion in the coolant sys­tem and help stop the fuel pump or water pump from stick­ing due to lack of use.

It’s worth bear­ing in mind that most heater fail­ures can be at­trib­uted in some way to in­stal­la­tion er­rors or ne­glect. The worst part about this is the heater is usu­ally re­moved, re­paired and put back on the same sys­tem that caused the fault in the first place.

Many thanks to Peter Col­lard, Eberspächer’s En­gi­neer­ing Project Man­ager, for his help with this ar­ti­cle

Blocked heat ex­changer due to lack of an­tifreeze

Sum­mer diesel reach­ing cloud point and start­ing to wax above 0C

Check the an­tifreeze mix

Don’t use ve­hi­cle si­lencers – they aren’t gas tight

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