Canal Boat Breakdown Guide

Canal boat insurance provider Towergate Insurance Marine has, with the help of breakdown and recovery specialist River Canal Rescue, listed the five most common canal boat breakdowns and how to avoid them.
This joint Canal Boat Breakdown Guide also offers general preventative maintenance and tool box contents tips, discusses how to solve problems before calling out a third-party and gives a word of warning about bio-diesel.


1. Fuel Issues and Contamination

Contaminated fuel due to Diesel Bug and water contamination accounts for most of the fuel-related breakdowns, securing Fuel Issues the top slot. The Bug is an enzyme that lives off water in diesel. In its mildest form it appears as black dust or soot, at its worst , it’s a black slime or jelly. Once in the system it clogs the engine’s fuel arteries and stops the engine working. Historically, the whole system would need to be cleaned to tackle the Bug, but River Canal Rescue uses a special fluid ‘Marine 16’ that prevents the bacteria from growing and kills anything that may be forming in the tank. One 500ml bottle treats 500 litres (enough for multiple treatments) of fuel and is suitable for mild cases or as a preventative measure. Towergate Insurance Marine gives away a 100ml bottle of ‘Marine 16’ to owners taking out its Fresh Water canal boat insurance policy. More severe cases (or when the fuel system is blocked) require a Diesel Bug shock treatment. We have a full page explaining the new diesel fuels and their implications.

Blocked filters and fuel contamination due to dirt and debris in the tank making its way through the fuel system also cause a large number of breakdowns – a situation that can be easily rectified through regular checking and servicing.

A word of warning – Bio diesel
Whilst River Canal Rescue is yet to collect conclusive proof, the firm has gone from replacing two injector pumps a year to 20 in the space of nine months. It is feared bio-diesel which is known to corrodes rubber seals is resulting in the increase in injector pump failing. RCR is monitoring the situation and will report back on trends, however in the meantime, the use of a fuel treatment additive like Marine 16, to help lubricate the system is recommended.


2. Batteries and Electrical

Common misunderstandings around what battery to use; its electrical capacity and charging levels and lack of attention to electrical connections contribute to batteries and electrical malfunctions taking second place.

Batteries – If you link leisure rather than a cranking battery to your starter system you could be left without power when you need it most.

Leisure batteries and cranking batteries are designed for different requirements. The cranking battery is the same as fitted to most vehicles and designed to deliver a high output quickly, it discharges and charges back to full capacity quickly. A leisure battery is designed to deliver lower output continuously and therefore as long as it’s charged regularly will maintain capacity. As a general rule, each battery in your battery bank will require two to three hours charging to get back to full performance once fully discharged, assuming that it is in a good condition. If the wrong battery is used, the sudden surge of power needed to start the engine can quickly drain capacity on a leisure battery and whilst regular charging helps to regain these levels, using this type of battery will eventually lead to battery failure.

It is worth mentioning that many ‘leisure’ batteries sold in the marine market are modified starter batteries and their performance, whilst suitable for owners who use the boat on a sporadic basis, can prove unreliable to more frequent users. For live aboard and frequent users it’s worthwhile investing in true leisure batteries such as those provided by Banner.

Most people do not realise that each battery cell can affect the whole battery bank, and one of the best ways to prevent battery deterioration is to regularly check and top up the water levels in the cells (using de-ionised water). If one cell’s water level drops to below 50%, it will affect the battery capacity and bring the battery bank capacity down to the same level, irrespective of how good the other batteries are. This is one of the best reasons never to mix and match batteries. Always replace the whole bank of old for new.

Ask the experts
Canal boat insurance provider Towergate Insurance Marine has joined forces with breakdown and recovery specialist River Canal Rescue to produce a Guide listing the five most common causes of emergency call-outs and how to avoid them. Thanks to them for permission to reproduce extracts here.
The Guide has been written in a bid to reduce the increasing number of people requiring rescue support and is available online at www.towergateinsurance.co.uk (click on boat, then boat tips) and www.rivercanalrescue.co.uk (click on tips and advice).


Similarly, battery terminals should not be forgotten – if they’re tight and greased they’ll deliver a good connection. It only needs one loose terminal to cause engine failure and usually the main earthing cable (connected to the engine bed) is the culprit.

Electricals – On a similar vein, wires coming away or corroding is a common fault, so again, visually check and look for loose connections or disconnected wires before you journey.

3. Breaking Cables

In third place, Breaking Cables takes a bow. This is primarily due to their exposure to the elements as most of the cable terminus is set outside. Cables only have a certain life-span which means if they’re not used regularly, they’ll rust. To prevent this, you can grease the ends of the cable if leaving the boat for long periods of time, and always check operation before you set off; if there’s any roughness or stiffness then it might be time to call into a marina to pick up a new one. When fitting, make sure that any bends in the cable are as minimal as possible as these will be the areas which suffer high stress and are likely to fail in the future.

4. Over-heating and Cooling Systems

Fourth place goes to a failure in the cooling systems which lead to the engine over-heating. The most common cause is due to an air-lock in the system which is simple to identify and resolve. To identify if this is the issue, feel the top and bottom of the swim tank, if everything is working fine there should be a difference in temperature, if not then both top and bottom will be hot or cold. To remedy this, locate and unscrew the bolt that sits on top of the ‘swim’ tank and this will release the air locked in the system. However overheating can be caused by many issues from a coolant hose rupturing, (look for leaks) a water pump failing or a fan belt shredding (which drives the water pump) or worse case, a head gasket failing.

5. Gearbox/Drive Plate Failures

An increasing number of boats hitting underwater objects have resulted in gearbox and drive plate failures entering the canal boat breakdown ‘top five’. The drive plate is usually the first victim of an underwater collision and accounts for at least one River Canal Rescue call-out a week.

A collision of this nature cannot be avoided and if the drive plate is damaged, it’s unlikely you’ve damaged your gear box. General wear and tear appears to be another cause – and because canal boats don’t have a clutch arrangement (they either go into gear or reverse), gear boxes tend to receive a fair bit of abuse, so go easy and regularly service them – they’re simple to check but expensive to repair. If you lose drive check the oil and top up if necessary – be careful not to overfill as you will experience the same symptoms as too little oil.

Before you make that emergency call
Below are some common scenarios which may help you solving the problem before making that call;

If you are losing propulsion and the propeller is slow-moving, put the engine in reverse.  The prop may be covered in weed or leaves and this can help release it.

If the engine cuts out when in gear, check the propeller for obstruction.

If the engine cuts out when revved, check the air filter – it may be blocked with dust (can be removed and run without it in an emergency).  Alternatively check for blocked fuel filters (Vetus has a small fuel pump filter that is usually overlooked).

Is the engine overheating?  It could be an air lock in the cooling system.  Resolve it by unscrewing the bolt sitting on top of the water tank – this will release the air.

If the boat won’t go into gear, check the cable is moving the selector arm on the gearbox, if it is then the cable is fine.  Check the oil in the gearbox.

Engine won’t turn off? Know where the manual stop button or lever is situated, usually on the right hand side of the engine.

All materials and images © Canal Junction Ltd. No unauthorised reproduction. Page last updated: 10/06/2022.

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