Rads downstairs go cold when HW is also on.

Hi guys hope you can help. I have a microbore CH system in my house, been having a few problems with a rad or two downstairs not getting as hot as the others in the house. Went through bleeding then balancing all the rads re instructions found on the web. All seemed OK after balancing felt pretty good about fixing this BUT just about to sit down for a cuppa and HW came on timer and noticed all my rads downstairs cooled right off, upstairs still v Hot. Noticed this was happening last week before balancing and I was hoping this may get fixed as well, but seems not. It never used to do this, any suggestions ? I have a valve in the airing cupboard labelled \\\"balance valve to primarys\\\" pipes seem to relate to hw/ch feed, could this need adjusting ?

You haven't properly balanced the system if all rads don't heat up even with hot water side on. You can close down the valve on the hot water circuit to force more flow to heating side, but better balancing would help too. Of course the pipes to the downstairs rads might be seriously undersized in which case you'll never get it right.

Obviously as the other chap mentioned the pipe work could be blocked. However, i think the most probable problem is you pump is getting weak. If it has a screw cap on the pump i suggest when it is running remove the cap (put a towel under the pump as water will come out) try to stop the propeller with a screw driver if it is easy to stop then it re- confirms that yes the pump has had its day.
I would say 99 percent of these problems i go to are always pump related.

if all rads don't heat up even with hot water side on.

Click to expand...

He meant OFF. Bless.

Try harder at balancing. Check the pump is on max speed (usually 3).
Pump could be tired, or more commonly, pipes/rads or pump, or everything, blocked a bit by sludge. Are the lower rads on "drops" to each one? If so these are particularly susceptible.

Thanks Guys will try a new pump, it does seem more noisy lately.
Cheers John