Top floor of town house gets hot, other radiators cold, ideas?

[Hariseldon]

I have a Glo Worm ultimate gas boiler on floor 1 of a four storey townhouse. I believe the heating installation to be original to the house, built in 1997, the system is open ,vented with a header tank in the attic. The pump Grundfos, controller and hot water tank on floor 4. There is a motorised valve allowing separate hot water , heating or combined. There are 5 radiators on the top 3 floors and 3 on floor 1, all using 10mm copper pipe. Larger pipe runs from boiler to airing cupboard and boiler and from pump into bottom of cupboard to go to radiators.

We moved in at the beginning of summer and the system operated fine and servicing had been cared out by a large local firm. All seemed well , although I noted that the radiators on floor 1 were lukewarm at best.

We moved a radiator on floor 4 , partially draining the system. We refilled the header tank, wiping it out. When the heating was put on I found only the top floor (4) had hot radiators, looking at previous posts here I loosened the bleed screw on pump, no indication of any air and tuned all bar 1 radiator off on floor 4, one radiator got hot on floor 3 , turned off the one rad on top floor 4 .
Another rad on floor 3 warmed up ,so turned off the first hot rad on floor 3 and repeated the process down the house till all radiators we're working , including the three previously Luke warm ones on floor 1.

All was well until a month later we had need to move a radiator on floor 1.
The system drained down, was pretty clean no sign of sludge, radiator removed was free of problems , ( not as much water came out as expected initially, but 10 minutes later the rest followed in short bursts! ) *replaced the corrosion inhibitor, turned on the header tank fill again, bled radiators and turned heating on again.

*I was not too surprised that only floor 4 got hot but the previous trick has not worked this time.......I have tried every variation I can think of with radiators turned on and off. ( all radiators on floor 4 turned off did not work and simply caused the boiler overheat protection to trigger)
I believe the pump is fine, as from a cold start all 5 radiators on floor 4 heat equally quickly and within about 2 minutes all are piping hot, I wouldn't have thought thermal circulation could do that as quickly and evenly, there is no one radiator heating up first.

Any ideas, I presume there is some firm of air lock......I am not very confident of previous heating engineer, reluctant to take pot luck with yellow pages.
There is probably a simple solution but I am struggling and the weather gets colder !*

 

[erj]

sounds like air lock. tricky to move try leaving the cold watrer on, drain the ch so the tank starts to fill, might move the air, might be then puled into rad, good luck.

 

[Hariseldon]

Thanks for idea, the thing is all the radiators appear to be full, ie bleed screw releases water, but I agree air lock is likely, presumably between floors 3 and 4.
I will give it a go but guess it may not be so easy as the water has made it down to the rads already by one route or another but it's not letting the hot water down when the heating is on.

 

[WHPES]

Is the pump functioning OK? Sometimes if they get jammed you get the upstairs working with gravity but the downstairs won't.

 

[Hariseldon]

Is the pump functioning OK? Sometimes if they get jammed you get the upstairs working with gravity but the downstairs won't.

Pretty sure the pump is working, as all 5 rads on the top floor get equally hot very quickly after turning the system on from cold.

 

[WHPES]

If you think its and airlock, close off the radaitors which work and try running it. You could shut all the radiators but one to force the air out, then go round them in turn.

 

[Hariseldon]

If you think its and airlock, close off the radaitors which work and try running it. You could shut all the radiators but one to force the air out, then go round them in turn.

The first time I had this issue, this is what I did and it worked but this time despite trying numerous times it is not working, the problem started after draining down to move a rad, as it did last time.

The system design appears to be weak in this respect.

 

[WHPES]

You probably need to get someone in. Look for an oldish guy who has been going for ages and seen it all!!

 

[Best]

If someone competent could remove a rad on any the circuits not working, when system cold, open valves into hose or bucket.

 

[Hariseldon]

If someone competent could remove a rad on any the circuits not working, when system cold, open valves into hose or bucket.

There are drain points on all 3 rads on floor 1, I could drain the system down partially and will do so tomorrow ,

 

[Best]

There are drain points on all 3 rads on floor 1, I could drain the system down partially and will do so tomorrow ,

No need to drain down system partly or fully. Just let water run from the circuits that are not heating. Mains pressure will clear airlocks, but this is strictly for a professional only & it has to not be put under any great pressure.

 

[Best]

Should have mentioned, just leave expansion tank filling water into system, as you run some water out of pipes/ rad valves. A minute or two each pipe. Dont need gallons water out. You might need a little inhibitor to add later, if this works.

 

[Hariseldon]

Should have mentioned, just leave expansion tank filling water into system, as you run some water out of pipes/ rad valves. A minute or two each pipe. Dont need gallons water out. You might need a little inhibitor to add later, if this works.

I'll give it a go and report back. Would it be sufficient to do 1 rad on each floor or all radiators ?

 

[Best]

I would try on each problem circuit just one rad - both pipes. Worth a try. Be careful not to flood the house! If rad valves are 15mm tails, & you use hose, then a small piece of copper into the hose with jubilee clip to secure, & a nut & olive on other end.

 

[stevetheplumber]

shut both valves remove air vent and let it run into a bucket one valve at a time till hot water flows to the valve id start with the lowest floor first

 

[Best]

Personally, I would prefer full flow of water through each pipe to try to clear air, even though it is harder than just working at rad air vent.

 

[dontknowitall]

Just because the pump bleeds doesn't mean to say it's working properly. The motor might be spinning but the impeller might be stuck still.

 

[Hariseldon]

Just because the pump bleeds doesn't mean to say it's working properly. The motor might be spinning but the impeller might be stuck still.

From a cold start, turning the heating on, there is instant audible movement of water, hot water hits the pump with 30 seconds and all 5 rads on the top floor are hot within 90 seconds or so. Seems unlikely that everything would be so quick if the pump was not working, given that a similar event occurred when a rad was removed and the pump was ok then I am reasonably confident that the pump is ok.

 

[BLOD]

Have the rads got trv's ? If so remove the trv's heads from the non working rads, open up the lock shields and close off the working rads - this might help chase the air out.

 

[RoryD]

Although your pump is turning, it may not be working as well as it should, perhaps the impellar is damaged or broken. It's possible that what you have is hot water convecting to the top floor and you aren't getting full circulation