Last Saturday I met up with a friend onboard his boat in Beaumaris North Wales where it has been ashore now for the winter since early in September. He had been onboard since the previous morning and had stayed onboard overnight to Saturday. When I arrived he said that he had not been able to get his diesel heater running. At first he had suspected that having separated part of the fuel supply line to the heater, that the line needed to be refilled. We took a few minutes to do that, and then operated the start control for the heater. It ran for a short while during which time the fan had started to increase speed, and then it shut down. It did this several times over a period of more than an hour, re-setting itself each time before eventually running up and continuing to run through until we decided that the heater was now running fine. After leaving I continued to think about why the heater had initially been reluctant to run for more than a few seconds at a time, but had noticed that run times on each occasion had been marginally longer each time the heater had fired up. At the time, It hadn’t crossed our minds that that the problem might have been down to fuel temperature, but outside temperatures overnight had been below freezing that night and for several days prior to the weekend. With the boat being out of the water since early September, the fuel within the diesel tank would have been exposed to much lower temperatures than a boat left in the water such that I had started to wonder if fuel temperature was the reason. Each time that the heater had fired up, it had added a little heat into the boat, and no doubt also to the temperature of the fuel within the fuel tank. Yngmar’s posted website reference I think has confirmed that fuel temperature most likely was the problem. Thanks Yngmar.