Can the plastic waste pipe on a dishwasher freeze? If it can, does it matter, given that it isn't completely full of water when not in use and any ice that did form would be able to expand along the pipe and not through the side of it?

Well I guess it can freeze if the room that it is in gets cold enough?! Although that would be unusual as that room is the Kitchen. Do you have an insulation problem or is the heating u/s?!

As for whether it would screw up the pipe - I dunno, but it should be a relatively simple thing to pull the dishwasher out and check the pipe over prior to use?

I would say it was very unlikely to freeze given that the water in the pipe should always be flowing. The only time it would, I guess is if there is a fault and the pipe holds water for a while.

Plastic waste pipes tend to just clog up with ice (as alot of condensate drains did this winter due to our lower than normal temps) rather than split, though it can happen.

In response to you (and to Falcore).

It's a strange situation. We had some new kitchen cabinets put in a while ago. They differed from the previous ones in that they are not right down to the floor at the back. In winter, we also smoke in the kitchen, under the range extractor. That thing is powerful enough to open doors in other parts of the house, so the smoke doesn't travel.

A couple of times this winter, the dishwasher has gone on the blink (not filling). We figured frozen pipe. On Saturday, we largely demolished the kitchen (counter tops, cabinets etc). We discovered the problem. The wall, while insulated, had a few small gaps at the bottom, where the drywall didn't meet the floor. The extractor was sucking in cold air wherever there was even a tiny gap. That was freezing the supply pipe.

We ripped off someof the drywall to make sure the wall was actually insulated. It was, so we re-drywalled. Sprayfoam was applied liberally. I also moved the supply line, to keep as much as possible of it on the warm side. The waste pipe would be a bastard to move and is still on the cold side, close to the wall. I don't want to move it unless really necessary.

Don't ask me how my weekend was.

In January 2008 when we had some really cold weather our washing machine waste pipe froze. The pipe froze where it entered the basement by the outside wall. The problem was caused by a small area that had been missed with insulation. We filled the gap with insulation and have not had any problems since.