Radiators cold at bottom

[Sam Egner]

Hi everyone

Looking for some advice please

I have Worcester Bosch green star 38cdi classic HB combi boiler.

It’s only a few years old and has a magni clean thingy fitted to collect the metal etc.

I have bled all radiators most rads bar 2 small ones 400mm x 400mm (old) are all brand new 2 panel 1 convector, all pipe work is 15mm no microbore

The upstairs rads get extremely hot almost too hot too touch, most the downstairs ones do as well apart from about 3 - I have turned all locksheilds down to virtually off about a quarter a turn open and these still get red hot. This improved the downstairs ones that were cool but still hasn’t solved the issue. Im wondering if I need a bigger pump fitted?

The rads have been taken off and flushed out there is no sludge issue here the boiler is only about 4 years old.

Does anyone have any suggestions or what it may be.

Thanks in advance

 

[Sam Egner]

This is my
Pump

 

[Aire]

Could be poor piping. How many rads on the system? Who removed the boiler cover to take the photo of the pump?

 

[Sam Egner]

Could be poor piping. How many rads on the system? Who removed the boiler cover to take the photo of the pump?

Poor piping in what respect?

I took the picture when I had a nest installed - the plumber who done it fitted me in between jobs so didn’t have a look at heating issue as wasn’t here long enough.

 

[Riley]

As mentioned above the cover forms a part of the combustion seal please call a gsr engineer to take a look and ensure the cover is replaced suitably

 

[Sam Egner]

Could be poor piping. How many rads on the system? Who removed the boiler cover to take the photo of the pump?

Sorry - there is currently 9 on the system with another 2 to be added when the rooms are decorated so these are capped off at present

 

[Riley]

Could be undersized pipework, could be two rads teed off the same feed, whilst unlikely it could be muck in the rads

 

[Sam Egner]

As mentioned above the cover forms a part of the combustion seal please call a gsr engineer to take a look and ensure the cover is replaced suitably

It was taken off and replaced by a engineer

 

[Riley]

All good then

 

[Sam Egner]

Could be undersized pipework, could be two rads teed off the same feed, whilst unlikely it could be muck in the rads

If I turn the rads off the the other one does not get hot etc so would this eliminate that suggestion?

 

[Riley]

Which suggestion?

 

[Riley]

What size pipework are we talking??

 

[Sam Egner]

Which suggestion?

Sorry mate the one about two rads teed off.

Also all pipe work is 15mm copper

 

[Riley]

No 22mm main carcass?

 

[Sam Egner]

If I turn all other rads off the cold ones get pipping hot but obviously I need them all on together and when I do the ones in question go cold more so at the bottom

 

[Sam Egner]

No 22mm main carcass?

Yes the pipe work to all rads is 15mm tho (sorry)

 

[Riley]

Itll be either teed off another 15mm feed and the pipework doesn’t have enough heat capacity to heat two rads or the system just needs balancing

 

[Sam Egner]

Itll be either teed off another 15mm feed and the pipework doesn’t have enough heat capacity to heat two rads or the system just needs balancing

I have turned all locksheilds on the radiators that get piping hot to virtually off like a very slight turn open and these still stay hot.

I assume this is how you balance?

The ones in question and in regards to them potentially being teed off are in various places of the downstairs and seems unlikely they could be teed off one another - clearly i don’t know and am not a plumber.

Is my suggestion about bigger pump or turning up something that would help?

 

[Aire]

You won't need a bigger pump, you've got 9 radiators so the pump in the boiler is more than adequate. Boilers 4 years old so unlikely needs the pump changing at all. Without us physically seeing the job it's hard to say but from what you've said, if balancing isn't solving the issue but your radiators work when everything else is turned off, it points to pipe sizing.

 

[Sam Egner]

You won't need a bigger pump, you've got 9 radiators so the pump in the boiler is more than adequate. Boilers 4 years old so unlikely needs the pump changing at all. Without us physically seeing the job it's hard to say but from what you've said, if balancing isn't solving the issue but your radiators work when everything else is turned off, it points to pipe sizing.

Ok thank you very much.

So if I have a 22mm main piping with 15mm pipes to rads.

What would be adequate pipe sizing?

Thank you

 

[Riley]

That’s adequate but if two rads are teed off one 15mm feed then it’s immediately splitting the kw out put

 

[Sam Egner]

That’s adequate but if two rads are teed off one 15mm feed then it’s immediately splitting the kw out put

I understand.

So assuming two of the rads that are not getting hot are joined together are teed off one another - turning one of these off should the other one then get hot?

 

[Sam Egner]

Also when one of you guys mentioned earlier poor pipe work do you mean size wise or did you mean like to pipes being run round to many bends etc like having to many elbows etc to go around or wouldn’t that effect it.

 

[Riley]

I understand.

So assuming two of the rads that are not getting hot are joined together are teed off one another - turning one of these off should the other one then get hot?

Theoretically yes

 

[Aire]

Also when one of you guys mentioned earlier poor pipe work do you mean size wise or did you mean like to pipes being run round to many bends etc like having to many elbows etc to go around or wouldn’t that effect it.

Well it could be either, as mentioned before we can't say for certain without seeing the job but you have poor flow to a couple radiators. Could be incorrect pipe sizing, could be too much restriction caused by numerous elbows in the pipe work. There could be isolation valves under the floor somewhere or a kinked pipe you may have faulty trv valves or partially blocked lockshieds. The list is endless. You've ruled out balancing and air locks. Consider taking the radiators off that aren't working and opening both the flow and return pipes to see what sort of flow rate your getting through the valve.