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!
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!
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.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!
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