Service
Canal Fuel Polishing Services
Canal Fuel Polishing Services
2 min read · Updated 2025-11-16
Canal Fuel Polishing Services
What this covers
Mobile and yard-based services that clean diesel in situ: pumping fuel out of the tank through fine filters and water separators and returning it clean, while removing the sludge, water and microbial growth (commonly called "diesel bug") that build up at the tank bottom. Most providers also clean the tank itself through inspection hatches, treat with biocide, and replace primary fuel filters.
What to look for
- Filtration down to at least 2 microns and a positive water-removal stage. Reputable operators publish their filter spec.
- A flow rate suited to a typical narrowboat tank (250–600 litres) — too slow and the job costs more than it should, too fast and dirty fuel passes the filters.
- Sample bottles taken before and after, ideally with photos, so you can see the difference.
- Tank-cleaning capability via inspection plate (or willingness to fit one), not just polishing the fuel that flows back to the tank.
- A clear position on contaminated waste — they should remove it, not dump it ashore, and provide a waste transfer note for any significant volume.
- Public liability cover and a fire-extinguisher present during work.
- Red flags: no sample shown, no biocide recommendation, willingness to skip tank inspection on a heavily contaminated tank.
Common questions
What is "diesel bug"? A community of microbes that lives at the diesel/water interface in the tank. It produces a black sludge that blocks filters and corrodes tanks.
How often should I polish? Every 2–3 years is a common interval for boats in regular use; sooner if you've had filter blockages, fuel starvation under load, or you've bought a boat with unknown fuel history.
Will adding biocide alone fix it? Biocide kills the bug but doesn't remove the dead biomass — that still needs filtering or pumping out.
Can I run on red diesel? On UK inland waterways red diesel is permitted for propulsion subject to the declared split between propulsion and domestic use, with full duty paid on the propulsion portion. Rules have changed in recent years; check the current HMRC guidance.
What does it cost? Typically a few hundred pounds for a standard polish, more if the tank needs deep cleaning. Cheap quotes that skip waste disposal often aren't.
When you need this
After a long lay-up, when you've experienced sudden engine cut-outs or filter blockages, before a long cruise, when buying a boat with unknown fuel history, or as routine preventive maintenance every two to three years.