Cold Radiators.... Running out of ideas

[neil33]

Since moving into a new house several months ago Im suffering from cold (cool) radiators in some of the downstairs rooms (3 out of 5 are problematic). Its a normal gravity fed system. This is what I have done so far:

All rads changed for new.
New TRV's and lockshields
System flushed (but not power flushed), cleaner installed (for few weeks) , flushed and refilled with inhibitor.
Magnetic filter cleaned and recleaned again after several weeks
Radiators balanced.
System bled.
Boiler serviced
New Pump

Most of the time the problem 3 radiators are only slightly warm but occasionally one will get hot but not for long.

Have tried closing off all the good rads and leaving the problem ones fully open and they do improve just a little.

Pipe on inlet side of the rads is red hot but cool on outlet side. Even tried slackening off the valve on the outlet side to make sure there was flow and there is (but maybe not enough?)

so Im running out of ideas now... surely if there was a blockage then the problem rads would never heat?

 

[ianmcd]

sounds like you may have a pipe sizing problem what size of pipe work for the problem rads and what size are the rads ?

 

[D_Hailsham]

1. Which pump do you have?

2. What procedure did you use to balance the rads?

 

[neil33]

2 of the problem rads are 4 bar column rads 60cm x 79cm 5000btu. The other 2 bar, 180cm tall x 40 column 3200btu, and all pipework 15mm.


One of the rads that is OK downstairs is also this size and heats OK

 

[neil33]

Just changed the pump today.

old one Grunfos UPS 15-50 130

New one DAB Evotron 60/130


Balance at closest rad upstairs to pump closed lockshield until just enough flow to heat the moved on to next nearest etc etc,

I am guessing that even if not balance correctly, by shutting off ALL of the good rads, the remaining 3 problematic ones should heat quickly?

 

[VictoriaHomeSolutions]

What type and size of bolier do you have? Maybe is not strong enough

Just changed the pump today.

old one Grunfos UPS 15-50 130

New one DAB Evotron 60/130


Balance at closest rad upstairs to pump closed lockshield until just enough flow to heat the moved on to next nearest etc etc,

I am guessing that even if not balance correctly, by shutting off ALL of the good rads, the remaining 3 problematic ones should heat quickly?

 

[D_Hailsham]

I am guessing that even if not balance correctly, by shutting off ALL of the good rads, the remaining 3 problematic ones should heat quickly?

True, but I would shut off all rads but one problematic one and see if that heats up OK; then repeat for the other two.

Try this balancing method.

The pump should be set to the middle fixed speed when balancing. This can be set to 3 if the average temperature drop across the rads is too large, or 1 if too small.

The pump can then be set to the normal working position

 

[neil33]

Boiler is a Worcester Bosch Grenstar 18Ri... its only a 3 bed cottage, & small rads up and 5 larger rads downstairs.

Pump is set to 3 at the moment but will try and rebalance on 2 and see if that makes any difference.

Have already tried shutting all of the rads off apart from one of the problematic ones..it does SLOWLEY get hotter but no where near the heat of a good rad.

Thanks for the input though guys...im open to any suggestions

 

[neil33]

Bit of an update...

Have shut all rads off apart from one of the dodgy ones... it now seems to be getting colder (?) boiler burns on/off/on/ etc Flow pipe from boiler Very hot, return pipe very cool.

...so don't know whats going on now!

 

[oldbuffer]

Are the new radiators "designer" type column radiators? Some of these require the flow and return to specific sides, they are not reversible, and if not correctly fitted won't warm up properly.

 

[easyflow]

Had a similar problem with an old system before christmas, found a major blockage cut some 22mm out but not much better, changed pump and flushed system still no good, pulled some floor boards and turns out the system was running on one pipe.
Converted to two pipe system and all rads came up a treat.

 

[neil33]

Are the new radiators "designer" type column radiators? Some of these require the flow and return to specific sides, they are not reversible, and if not correctly fitted won't warm up properly.

Yes that's a fair point... I knew the bleed had to be opposite the inlet side but maybe its worth turning them around to try. They can be reversed or turned upside down so will try when I get the chance. Thank you..

 

[neil33]

Had a similar problem with an old system before christmas, found a major blockage cut some 22mm out but not much better, changed pump and flushed system still no good, pulled some floor boards and turns out the system was running on one pipe.
Converted to two pipe system and all rads came up a treat .

I am starting to think its some sort of a blockage myself. I think its a two pipe system as the heating flow from the 3 port valve divides into two before disappearing under the floor boards and there also appears to be 2 rad returns.

Hope its not time to lift all the floorboards!

 

[twgas]

Any plastic pipe? If so i wouldn't be surprised if it's blocked/restriced

 

[neil33]

Any plastic pipe? If so i wouldn't be surprised if it's blocked/restriced

Yep..its all plastic pipe!

So how come plastic is more susceptible to blockage?