Radiators hot upstairs but cold downstairs

11 Feb 2008
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United Kingdom
Hi, was wondering if someone could give me some advice on what is causing my upstairs radiators to be hot but the ones downstairs to be cold (or at best, tepid)?

I have tested the pump and it seems to be working fine. When I switch on the CH I can hear it whirring, there is a vibration from the pump when you touch it and there is a distinct (low) sound of water being forced through it. It also gets pretty hot after a while, so I presume hot water is passing through it.

The other evening I switched all the radiators off upstairs and found the ones downstairs started to get hot! But as soon as I switch on the upstairs rads I get the same problem.

After a lot of testing TRVs and lock shields and bleeding radiators I'm left scratching my head.

Does the system need a powerflush? Is there a "radiator balancing" problem? Something worse?

Boiler: Ideal Mexico HE24 floorstanding, located downstairs with its timer/controller. Thermostat is in the hallway. Pump is in the upstairs bathroom - Grunfos Alpha+ with a Honeywell Sundial Y plan 3 position diverter valve. 7 rads upstairs, 4 rads downstairs.

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You may have it sussed with the balancing and flushing thing but it is most likely that your pump is on its last legs as well as the system needing a flush. Try turning the pump up a notch if you can. If its noisy then that will be an indication of its 'ill health'
If the upstairs radiators are v hot then try balancing the system but id have to agree with slug and say that it does sound as the pump is going.
had the same fault 2day, i choped out and cleaned the "h" and fitted a new pump 2be sure! ya neva no ya pump mite be o-rite, had it alot where the cold feed is jus partially blocked
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Had exactly the same prob recently, even replaced the pump......ended up solving the problem after taking up the floorboards above the point where the CH pipes went downstairs to check their layout. Discovered that when the CH was originally laid (19 yrs ago) the plumber had, just a couple of inches beyond the down and up pipes, put in a loop connecting the out and return pipes, thus creating a path of least resistance, so the hot water chose never to go downstairs but just kept circling upstairs. Drained system to below the level of this loop, chopped out a bit of pipe and blocked off the two ends et voila.....hope this helps.

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