New pump not all radiators working

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Hi folks, got what I think is called a system boiler. It fired up for hot water and heating but then cut out within seconds. Changed the pump ( a lot of water came out even though I had tightened both isolation valves above and below pump ) All is good with heating and hot water now. Only problem is before the initial pump problem all radiators worked. After the new pump was fitted all the radiators work apart from two downstairs (the other four downstairs ones work). One pipe leading to the radiators is really hot but the other is cold. I`ve bled them and there appears to be no air. One radiator is old but the other one is not all that old.Any help would be great, cheers.
 
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Could be an air lock in the pipework somewhere. Is the CH system fed by a cistern in the loft or is it sealed, where you have a red expansion vessel and the system is topped up by opening a valve?

Try turning off all the rads and ensure both valves to the 2 that aren't warming up properly are open and just run them. How many rads do you have? Did you balance the system?
 
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As per MadRab, did you balance the system? I doubt very much that you have a system boiler; the pump for those is usually within the boiler casing.

I'd also add to Rab's advice, turn off all the working rads and see if that makes a difference. If it does then balance the system, using the guidance elsewhere on this site.
 
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Did as you guys suggested with the rads and all works perfectly. Cheers for that.

As for a system boiler i think I was totally wrong , as I`ve got a hot water tank fed from a header tank and the pump I replaced is in the airing cupboard next to the tank. Once again thanks Guys
 
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Still need help ! As I stated earlier all was working well, next time heating set to come on all rads cam on apart from the same two as before. Switched all working ones off again and started heating the two worked switched others back on and the next day when the heating came on on timer the same again , all working but the two still not. Cheers
 
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Did you balance the system ,or just turn other rads off ,until problem two heated up,and then put others back on ?
 
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Still need help ! As I stated earlier all was working well, next time heating set to come on all rads cam on apart from the same two as before. Switched all working ones off again and started heating the two worked switched others back on and the next day when the heating came on on timer the same again , all working but the two still not. Cheers
Do you have TRVs? If so maybe the cold 2 will warm up after a while, when the TRVs on other rads throttle down. If not, you need to throttle some or all of the other rads on the iso valves. But likely to want to be less than one turn from fully closed, just turning the valve a couple of turns won't be enough.
 
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I just turned the rads off as I don`t know what balancing the system means and also I don`t know what TRV`s are.
 
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I just turned the rads off as I don`t know what balancing the system means and also I don`t know what TRV`s are
If you're not sure what this stuff is then you may find it difficult to set up your heating system properly. You may need a recommended Central Heating engineer in to set everything up for you and get it all working properly.
 
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I`ve just looked up TRV and yes I do have one but only on 1 rad of the 2 in the downstairs bathroom. Before I call anybody in as my son is very ill and we have to totally isolate I would like to try and sort it. Also the rads that don`t work are the ones in the dinning room and living room, if I leave the dinning room one on and switch off the bedroom one above it when the heating comes on in the morning the dinning room one works fine.
 
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I`ve just looked up TRV and yes I do have one but only on 1 rad of the 2 in the downstairs bathroom. Before I call anybody in as my son is very ill and we have to totally isolate I would like to try and sort it. Also the rads that don`t work are the ones in the dinning room and living room, if I leave the dinning room one on and switch off the bedroom one above it when the heating comes on in the morning the dinning room one works fine.
Just throttle down the rads which are getting hot, and the problem rads should warm up. As I said before, the valves likely to need to be almost fully closed, but not quite unless you're happy for no heat from that rad. Set the TRV to the setting you want, probably about 3, but if there are 2 rads in the room, at this time of year might be OK turned right down.
You might need to trim the valves several times over a few days to get everything balanced properly.
 

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