random cold radiators and temperamental hot water

Hello. I 6 month old Vokera combi boiler which was great until a month or two ago. Now I have apparently random radiators that don't work (pipework to and from cold) of which 2 are downstairs and 1 upstairs. I've tried bleeding them but only get nice clean water out the top. I've also checked the thermostat valves and the pins all move freely.

The hot water is also running hot and cold which makes for an interesting shower experience, particularly as one of the dodgy radiators is in the bathroom.

Any ideas? If the problem is sludge, will draining the system and adding a cleaning agent for a couple of days be sufficient or will it need a power wash?

Yours shiveringly,

Sunshine girl

Sounds like sludge. Is your boiler 6 months old? In which case (1) did the installer flush the system when installing? and (2) is it not still under guarantee (installer's and manufacturer's)?

Sludge can be flushed out in various ways, some cheaper than others. Power flushing tends to be expensive, but in my view is not necessary (others may disagree, especially those who own power flushing machines). I would use mains pressure water, but the boiler HW heat exchanger may need separate cleaning.

Thanks Chris. I'll try flushing out this weekend and will call the installation engineer if that doesn't work.