They may have cracked. You need to put anti freeze in each year. We have been advised to do it in October. Luckily we didn't sustain damage before we were told. And we had had some very cold nights. Sadly not everyone was as lucky.
I think it was bad that we weren't told when we moved in. I wonder what the position would have been had damage resulted.
Best wishes to you and I hope it isn't too bad.
