jonandshell Dec 12, 2010
We too had the same problem with our unit. We contacted our local dealer who then referred us to Webasto technical who were brilliant! They called us back at 6pm on a Friday night and talked us through the problem!
The newer owner's manuals for the dualtop detail a descaling proceedure using white wine vinegar. We used malt, but what the hell! It worked!
The valve, however, was still sticking. Like everything else that sticks, I reckoned it needed working to free it off.
I must emphasise the following advice is not from Webasto!
If you hold the selector dial on the control panel to the left and hold it in the manual drain position, the valve will operate every five seconds.
Clip a pair of molegrips lightly on the switch, holding it in that position and go and watch Eastenders! During your break, the valve would have been open and shut 180 times, thus freeing it off and allowing it to seal once more!
We live in a hard water area and wild camp a lot. Thus we always fill our water tank before we go. A 6 monthly descale looks like a small trade-off for having an otherwise brilliant heating system!