Radiators don't get hot. Broken pump, divertor valve or...

[dominoman]

I have just moved to a new house and have spent every weekend finding nasty surprises that we didn't know about...

On Monday I turned on the central heating, crossed my fingers and... No joy.

One radiator next to the track gets hot. All the others upstairs are stone cold, and downstairs are slightly warm.

I've tried bleeding and is not that. The radiators are the same temperature to and bottom.

My theories are broken pump, broken diverter valve, or a broken controller.

Would love to get some opinions on what to do first. I've never touched plumbing before so have read everything I can on these forums.

One thing that is odd is the pump gets really hot even when the pipes into it are cold. Also the boiler is firing almost constantly even when the timer switch is set to off.

Any ideas to try would be great. I'm thinking to replace the pump and divertor first?

 

[oldbuffer]

If the pump is hot even when the pipes are cold its because the pump is not rotating. It could either have a stuck rotor or the start capacitor has failed:

a. Take the big chrome screw out of the end (assuming Grundfos pump or similar), old towels / container down to catch water which shouldn't be much. Screwdriver into the now empty screw hole and spin the spindle. With luck the pump will start. However, if this is the problem I'd start saving for a new pump.

b. If you really know what you're doing with electrics, replace the capacitor. Isolate the pump first (probably the main switch for the boiler, but not always so check with a multimeter / good quality voltage detector first. Remove plastic cover to pump electrics. Check again for no voltage. Remove old capacitor and replace with a new one. Usually 2 microfarads, but rated for AC mains. Try Maplin but make sure it will physically fit. On Grundfos its easier to cut old wires and join to new ones of new capacitor. I don't think polarity matters as its AC, but join like for like just in case.

 

[dominoman]

Many thanks. I'll try that when I get home tonight. If I can fix the pump then I can move on to the next problem - and perhaps it will even fix the randomly starting boiler somehow.

The whole system looks properly knackered. But I can't afford to replace it yet.

 

[dominoman]

It turned out the pump was the problem. I did as suggested, took the central screw out of the pump and could see it wasn't spinning when on. With a bit of twisting it it has freed up and now seems to be working!

The next problem is the radiators are very cool at the bottom, even after leaving the heating on a long time - so I'm going to drain the system and then refill with some Sentinel sludge remover

 

[kbdiy]

While the system is drained it would be worth flushing the rads through with a hose, then give it a chemical clean. At least that way will get rid of most of the muck rather than pushing it round the boiler and pump.