Central heating issues
Discussion
Wonder if any of the plumbing guru's have any thoughts on this one for me!
Our CH system is less than 5 yrs old, pretty much all of it was replaced with the exception of a few (checked) pipes.
The last couple of weeks with the cold snap it's obviously been under a lot greater strain, which is probably highlighting the problem, but basically none of the downstairs radiators are heating up properly. The tops get warm/hot, but the bottom of the radiators stay comparatively cool - Top edge of the radiators is at 60 deg, bottom is at 50 deg (if that, and it takes ages for them to get to that at the bottom) Boiler water temp is set at 75 deg. I've tried shutting off all the upstairs radiators completely and still the same result, so not a balance issue? It took 6 hours to get the downstairs temp from 19 deg to 20 deg C.
The result is a house that's hot upstairs and like a fridge at the bottom!
Our CH system is less than 5 yrs old, pretty much all of it was replaced with the exception of a few (checked) pipes.
The last couple of weeks with the cold snap it's obviously been under a lot greater strain, which is probably highlighting the problem, but basically none of the downstairs radiators are heating up properly. The tops get warm/hot, but the bottom of the radiators stay comparatively cool - Top edge of the radiators is at 60 deg, bottom is at 50 deg (if that, and it takes ages for them to get to that at the bottom) Boiler water temp is set at 75 deg. I've tried shutting off all the upstairs radiators completely and still the same result, so not a balance issue? It took 6 hours to get the downstairs temp from 19 deg to 20 deg C.
The result is a house that's hot upstairs and like a fridge at the bottom!
I'm no expert, but it sounds like your system has sludge in it (settles out to the bottom.
You need to drain the system, and let it run through, to get the rubbish out. When you refill, make sure you put inhibitor in it.
I had the same problem with a couple of my radiators. When I got some others replaced, and the system had to be drained, the problem went away, and the plumber commented on how black the water was.
Regards
Sparks
You need to drain the system, and let it run through, to get the rubbish out. When you refill, make sure you put inhibitor in it.
I had the same problem with a couple of my radiators. When I got some others replaced, and the system had to be drained, the problem went away, and the plumber commented on how black the water was.
Regards
Sparks
It sounds as though your system needs balancing. This is where the black magic & a little trial & error begins...each upstairs rad will have a valve on each side. You need to be closing the "lockshield" valve on each rad. This is the one that has a small cap on it & requires a pair of grips for instance to adjust.
Shut each upstairs radiator lockshield off fully. Run your system for a while & see if the downstairs rads are heating up fully. If they are this rules out sludge etc. In turn, open the lockshields on the upstairs rads. Open them half a turn at a time, you want them open just enough to allow the heat to come through.
Water is lazy & will go where it's easiest to get to...as it's 80degrees or so it'll want to rise, hence the upstairs rads getting all the heat. By restricting flow to these upstairs rads you're in effect making it more difficult for the water to get up there & hopefully persuading it to go to your downstairs rads.
Also, turn up the pump speed if it's on a lower setting, usually a 3 speed selector switch on the side of the pump. Try it one click at a time see if that helps.
Shut each upstairs radiator lockshield off fully. Run your system for a while & see if the downstairs rads are heating up fully. If they are this rules out sludge etc. In turn, open the lockshields on the upstairs rads. Open them half a turn at a time, you want them open just enough to allow the heat to come through.
Water is lazy & will go where it's easiest to get to...as it's 80degrees or so it'll want to rise, hence the upstairs rads getting all the heat. By restricting flow to these upstairs rads you're in effect making it more difficult for the water to get up there & hopefully persuading it to go to your downstairs rads.
Also, turn up the pump speed if it's on a lower setting, usually a 3 speed selector switch on the side of the pump. Try it one click at a time see if that helps.
Edited by andySC on Monday 6th February 13:28
It's a single zoned house, I did initially wonder if the water / heating valve was stuck (had before) but couldn't see any reason why it would affect downstairs only! I've had it apart and tested anyway, that all works.
I'd be a tad surprised if it were sludge, given that it's all nearly new and has been flushed through plus inhibitor, in fact thinking about it last time it was flushed through was when we changed a rad only 3 yrs ago! I guess you could be right but I'll be a bit worried if it is that.
I've already tried balancing it - no change, you simply can't get the downstairs rad's to be of relatively even temperature top to bottom even with upstairs completely shut off - hence my confusion!
I'd be a tad surprised if it were sludge, given that it's all nearly new and has been flushed through plus inhibitor, in fact thinking about it last time it was flushed through was when we changed a rad only 3 yrs ago! I guess you could be right but I'll be a bit worried if it is that.
I've already tried balancing it - no change, you simply can't get the downstairs rad's to be of relatively even temperature top to bottom even with upstairs completely shut off - hence my confusion!
Must be a blockage if it's all one zone, a newish system and some rads will heat up fine.
If it were upstairs with the problem it could possibly point to poor flow or a dodgy pump - downstairs suggests otherwise.
There's no gate valves hidden away somewhere after the flow or return splits to go upstairs is there?
I'd find the main flow/return pipes where they split and see what they do when the system fires up - does the upstairs branch immediately feel much hotter? It'd have to be a big chunk of crap to block what is presumably a 22mm pipe. Pump speed fiddling as above may help.
No, I'm not an expert
If it were upstairs with the problem it could possibly point to poor flow or a dodgy pump - downstairs suggests otherwise.
There's no gate valves hidden away somewhere after the flow or return splits to go upstairs is there?
I'd find the main flow/return pipes where they split and see what they do when the system fires up - does the upstairs branch immediately feel much hotter? It'd have to be a big chunk of crap to block what is presumably a 22mm pipe. Pump speed fiddling as above may help.
No, I'm not an expert
Davi said:
I've already tried balancing it - no change, you simply can't get the downstairs rad's to be of relatively even temperature top to bottom even with upstairs completely shut off - hence my confusion!
Did you have the hot-water off and any bypass valve shut? Is it multi-dropped or just one big drop. If it's the latter I would shut every radiator with the exception of one downstairs near to the drop. If there's air at the top of the flow of a drop it may still circulate, but at a very reduced effort. Ferg said:
id you have the hot-water off and any bypass valve shut? Is it multi-dropped or just one big drop. If it's the latter I would shut every radiator with the exception of one downstairs near to the drop. If there's air at the top of the flow of a drop it may still circulate, but at a very reduced effort.
Hot water off, yes (second time... I may have forgotten first time!) Do you mean the hot water / heating valve? If so yes, that was shut so it was to heating only (checked that as had issues with the motor in the valve before). It's is a multi-drop - in fact only 2 downstairs radiators share a drop at all.
Ferg said:
Yeah, make sure the hot water valve is shut. It's a 2x zone rather than 1x mid-position? Is there a bypass valve?? There pretty much should be. Either auto or a gatevalve on a pipe joining the flow after the pump to the return. Try all the effort on one drop.
It's a single 3 port mid-position valve. Not sure on the bypass valve, none that I know of!!! 
(I'll get lynched if I turn upstairs off while the minime is asleep LOL) Cheers Ferg.Have you fully opened all the lockshield valves on the downstairs rads? Just closing the upstairs ones wont help with a balance problem if the downstairs ones are virtually closed anyway.
Best thing to do is close everything apart from the rad nearest the boiler (by pipework route), then open others one at a time and see what happens.
Best thing to do is close everything apart from the rad nearest the boiler (by pipework route), then open others one at a time and see what happens.
yeah all lockshields downstairs were fully opened.
I've completed the 'close all bar one' test of Ferg's suggestion - Rad did get hot a bit quicker and more evenly!
One thing I have just noticed though - I have to get everything 'basically' working every night once I've finished playing (have a 3yr old so wife isn't happy about having them all off in -7 deg weather...) With everything upstairs *just* cracked open, downstairs being pretty much wide open throughout, I checked the temp of the flow and return to the boiler. There is a considerable difference in temperature between the two - return is really quite cool?
Would that not suggest pump issues? I thought pumps either worked, or didn't work? it's definitely pumping and on the highest speed!
I've completed the 'close all bar one' test of Ferg's suggestion - Rad did get hot a bit quicker and more evenly!
One thing I have just noticed though - I have to get everything 'basically' working every night once I've finished playing (have a 3yr old so wife isn't happy about having them all off in -7 deg weather...) With everything upstairs *just* cracked open, downstairs being pretty much wide open throughout, I checked the temp of the flow and return to the boiler. There is a considerable difference in temperature between the two - return is really quite cool?
Would that not suggest pump issues? I thought pumps either worked, or didn't work? it's definitely pumping and on the highest speed!
Davi said:
yeah all lockshields downstairs were fully opened.
I've completed the 'close all bar one' test of Ferg's suggestion - Rad did get hot a bit quicker and more evenly!
One thing I have just noticed though - I have to get everything 'basically' working every night once I've finished playing (have a 3yr old so wife isn't happy about having them all off in -7 deg weather...) With everything upstairs *just* cracked open, downstairs being pretty much wide open throughout, I checked the temp of the flow and return to the boiler. There is a considerable difference in temperature between the two - return is really quite cool?
Would that not suggest pump issues? I thought pumps either worked, or didn't work? it's definitely pumping and on the highest speed!
Have you bled the pump?? There's usually a screw on the front of the pump to let air out.I've completed the 'close all bar one' test of Ferg's suggestion - Rad did get hot a bit quicker and more evenly!
One thing I have just noticed though - I have to get everything 'basically' working every night once I've finished playing (have a 3yr old so wife isn't happy about having them all off in -7 deg weather...) With everything upstairs *just* cracked open, downstairs being pretty much wide open throughout, I checked the temp of the flow and return to the boiler. There is a considerable difference in temperature between the two - return is really quite cool?
Would that not suggest pump issues? I thought pumps either worked, or didn't work? it's definitely pumping and on the highest speed!
annodomini2 said:
Have you bled the pump?? There's usually a screw on the front of the pump to let air out.
had a problem with that before, nothing this time.Ferg said:
No. Pump motors can wear and not give anything like the effort. You may have any number of the impeller vanes full of crud. You can't assume anything with the pump!!!
Bugger! It's only 5 yrs old too 
maybe I'll take it apart once the temperature outside is above freezing! Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff