We bought our house a couple of years ago and it has a very old Baxi back boiler and hot water cylinder in the airing cupboard - with no thermostatic valves on any of our radiators. We've slowly been installing valves as we've redecorated rooms but not all of them have them on yet.
Until recently whenever the hot water came on, the radiator in the bathroom heated up at the same time, making all of our towels toasty and warm. However recently the bathroom radiator hasn't been heating up but the rad in my DC's bedroom has been instead. If I turn that radiator off (manually, using a pair of pliers...) it goes back to heating the bathroom radiator, but obviously with the weather getting colder I don't want the radiator in the bedroom turned off. It's not such an issue over the winter as the heating and HW come on using the same timescales (we have a very old analogue timer too), but in the summer it's a problem as it makes the bedroom exceedingly hot.
Does anyone have any suggestions what it might be and how I can fix it? We haven't made any material changes to the system very recently except to install a TRV to our bedroom radiator. Could this have done it?