A no start on the day you want to go cruising is one of the most common callouts on the Thames. Nine times out of ten it is something simple. The trick is to work through possibilities in the right order rather than guessing, so you do not flatten a battery or flood an engine while you investigate.
First, listen carefully
Turn the key and pay attention to what the engine actually does. Silence, a single click, a slow lazy crank, or a healthy crank that simply will not fire all point to different problems. Match what you hear to the right branch of the checklist below.
Silence or a single click
- Check the battery isolator is on and the start battery is selected.
- Look for corroded or loose terminals on the start battery and starter motor.
- Test resting voltage. A healthy 12V start battery should read 12.6V or more.
- If voltage is fine but you only hear a click, suspect the starter solenoid or a poor earth back to the engine block.
Slow, lazy cranking
This is almost always battery related. Old batteries fail under load even if they read 12.6V at rest. Cold mornings make it worse. Try the engine on the linked house bank if you have an emergency parallel switch. If it spins healthily on the other bank, the start battery is the problem.
Cranks well but will not fire
- Confirm there is fuel in the selected tank and the fuel valve is open.
- Check the primary filter bowl for water or sediment.
- Bleed the fuel system if the boat has been laid up or you have changed a filter.
- Inspect the stop solenoid or stop cable. If the engine thinks you are telling it to stop, it will not fire.
When to call a mobile engineer
If you have worked through the basics and you are still stuck, get in touch. Most no starts I attend on the Thames are resolved in a single visit at your mooring, with no need to move the boat. Breakdown callouts are available across the river from London to Oxford.
