Some radiators not getting hot

[Zochus]

Hello guys, for quite some time I have had annoying issue with my central heating system but I'll write some background to explain that a little bit more.

So we have bought our house last year in september and done a full refurb in it meaning we removed all the radiators as well to get them moved from very inconveninent places in the room undernath the window (which should be obvious when they were installed the first place). We have also added 1 extra radiator to the system and changed another one for a vertical one.

We have 4 radiators upstairs: 2x single panel 120cm, 1x single panel 90cm and 1x single panel 60cm
Theres also 5 radiators downstairs: 2x Double panel vertical 180cm high double panel, 2x double panel 70cm and 1x double panel 40cm.

The 2 vertical ones that are now separate used to be a single 180cm single panel radiator but since now kitchen and living room is an open plan and vetical units are much more space efficient we had to add these instead.

At first for first week or so it was all fine while we did the finishing jobs and were putting the laminate flooring all around the house. The vertical radiators took slightly longer to heat up but I assume thats normal since they are quite high and all the other radiators were heating up quick and were boiling hot. the central heating used to work for 10 hours a day at then since we were in and out the house and it was january so quite cold. Also everything like paint had to dry up fairly quick. Then the problems have started at which point no changes were made to central heating since it was working just fine. Once heating is on all the radiators downstairs get hot but upstairs when all are on then the two 120cm ones only get half hot wich is jut the top part and its not even hot but warm. Although if 90cm one gets turned off aslong with 60cm then the bigger ones get hot immediately.

I have had all the radiators checked and even replaced the two 120cm for new ones since we thought theyre blocked but theyre not in fact. Pressure seems to be strong at all pipes upstairs when we took every single radiator off to check if there's a flow which is flawless. System has been drained and cleaned seveal times and its all clean as far as we know but problem still occurs.

I have to get it sorted as soon as possible since the temperatures as off last night got quite low and we need to start heating the house up. befre that we had the two radiators turned off as the reception room is fairly warm usually during the day and not used often as well as the toilet which has small radiator but we are at the point where all radiators need to work at full heat.

I suspect the pump is not powerful enough or it is giving up but i need an option and suggestions of those who are more skilled and with far better nowledge than myself.

The combi boiler is situated downstairs undernath the stair case and it's a Main Combi 30 Eco wih Grundfos UP 15-60 A0 pump. I thought the pump has 3 peed settings and it might be set to the lowest one but I took the front cover and it turns out its just a basic pump without the option to change its speed so has only P1 setting at which it runs at 90W.

Any suggestions are much appreciated and if there's anything I missed please let me know as I am now desperate to sort things out, nobody wants to wake up to cold house.

Thanks a lot in advance and thanks for any help given.

 

[chris1982]

Balancing through lockshield valves?

 

[Zochus]

Balancing through lockshield valves?

Any more details on that please?

I think I've got that right, so the radiators closest to the combi should have lockshield set to almost off while the furthest away frm it should be fully open. I will get that checked and hetaing on later on in the afternoon once I come back home and see if that does any good. I hope thats as simple as that.

 

[HassV]

I agree, balancing them may work. When I moved into my current house, 3 of the upstairs radiators were always cold, turning down the downstairs ones and fully opening the upstairs ones solved the issue...a bit of trial and error was needed to get it right.

Also, have you tried bleeding them, you say the bottoms are getting hot, that could be a sign of air in them, you may have a small leak somewhere that's getting air in the system, this would naturally find its way to the tops of the radiators.

 

[Zochus]

I agree, balancing them may work. When I moved into my current house, 3 of the upstairs radiators were always cold, turning down the downstairs ones and fully opening the upstairs ones solved the issue...a bit of trial and error was needed to get it right.

Also, have you tried bleeding them, you say the bottoms are getting hot, that could be a sign of air in them, you may have a small leak somewhere that's getting air in the system, this would naturally find its way to the tops of the radiators.

I will try balancing them later on but it's the top that gets hot while bottom stays cold which is strange. I have bleed them all.

 

[D_Hailsham]

I doubt if the pump is too small; the problem is probably that the system has not been balanced correctly.

Your boiler is designed to work with a temperature difference of about 20°C; older boilers required a 10-11°C difference. The difference is inversely proportional to the flow rate (litres/sec), so a 20°C difference requires half the flow of a 10°C difference. Halving the flow reduces the friction loss in the pipe work by a factor of 4, so the head is much smaller.

As your boiler has a fixed speed pump, you are unlikely to obtain a differential of exactly 20°C. So you need to aim for a differential which is the same for all radiators.

 

[D_Hailsham]

I have bleed them all.

Bleeding should be done with the boiler off and the water cold. Always bleed the ground floor first, then the first floor.

 

[Zochus]

Bleeding should be done with the boiler off and the water cold. Always bleed the ground floor first, then the first floor.

Yes all radiators were bleed while combi was off and they are fine. I have tried the balancing thing and turned down the radiators downstairs while upstars 120cm ones are full on and the others are half open. Maybe should I turn down the 120cm ones a bit so there's a pressure on the valve making it heat fully? Im not sure but at least all radiators are now hot to certain point.
However the 120cm in one of the bedroom is still colder at the bottom while its hot at the top which bugs me a bit as I cant seem to find an answer to this myself...

Positive side is that when i got home afternoon temperature was 16 degrees celsius and after an hour of heating whole house is back at 21 degrees pretty much.

 

[D_Hailsham]

Adjusting a lockshield valve by half-turns is much too coarse; 1/12 turn is more like it. You have to wait 5 minutes for the effect to be noticed.

if you don't have a suitable thermometer, use your hand to compare the temperature of the return pipe (that's the cooler one) of all the radiators. They should all be the same.

1. Start with all TRV heads removed and any wheel valves fully open.
2. Set all LS valves to 1/2 turn open.
3. Set room stat to a high temperature so boiler will keep running.
4. Let the system warm up
5. Check the return pipe temperatures on all rads.
6. Close the LS valve of the hottest one by 1/12 turn
7. Wait 5 minutes
8. Repeat from 5 until all rad returns are approximately the same temperature.