The boiler is broken and we have no hot water. Where do we stand as tennents?

Our boiler has broken and the repair man said it may take upto 3 or 4 days for the parts to come in. We are private tennents, and it has already been 3 days, meaning we will have been a week with no hot water by the time we get it fixed. I'm considering asking if we can knock 10-15% off next month's rent as we have been travelling 20 miles and back to my parents house for baths every day. Where do we stand? UK only please.