Truma combi drain down

It’s the same boiler on our MH. It could be the breather elbow, situated at the top of the tank on the pipe where the hot water leaves the tank. This lets air in when the tank drains. We have the opposite problem in that it sometimes doesn’t close properly when we fill the tank and we get a constant drip from the breather tube. I’ve replaced it once, when it wouldn’t close at all. It’s a very poorly made cheap plastic part that Truma charge a ridiculous amount for. Removing it completely would allow you to drain the boiler as a temporary measure, in case we get any more freezing conditions.

Just to add, you would want to open the taps and  drain what you could out first to get rid of the pressure.

We did have a similar problem many year ago now and I recall another poster a while back with the same problem.

It might discharge as you go home or another site as ours did once but the yellow drain value had to be replaced, an easy job if you're technically minded but ours was done under warranty at the dealer very quickly.

It won't hurt to tow (are you a caravan?) with it full but as Steve alluded to it might do some damage in a severe frost which wouldn't be covered by any warranty.  

As mentioned above, it's quite an easy job to replace the breather which Steve mentions and also for goo measure swap out the yellow drain valve for good measure.

Just remember not to open that drain valve if you're on a grass pitch. I spend many hours trying to repair damaged pitches from hot water.

JK