luke warm radiators help!!

[stefbacardi]

i have a problem whereby two rads downstairs only become warm and at the bottom of the rad its still cold. They are brand new and a week before i had already flushed the system with fernox. I have balanced rads, checked trv's are working, boiler is running 1.5 bar and is at 65 degs. What i have noticed is that the flow temp to the rads in question are abt 60/62 deg but the return is abt 30 deg !!!! Does this meen the pump is failing ??? Can anyone please help me
many thanks

stef

 

[corgiman]

How did you flush it

cos it sounds like it hasnt worked

 

[JohnD]

and how did you balance them? cos that doesn't seem to have worked either.

If you want to, yoiu can tell us about your system (see //www.diynot.com/forums/viewtopic.php?t=6026

and tell us why you fitted new ones

did the old ones work

what is the pipework to these two rads

what happens when you turn off all the hotter rads

have you got a by pass

have you got a hot water cylinder, and is it surprisingly hot.

 

[stefbacardi]

I balanced the rads by isolating all rad valves first and then opened the nearest first by a quarter/half turn gradually increasing till i got to the furthest rad.
I flushed the system myself by leaving fernox in for a week as sugested and then opened drain cock down stairs and drained system. Once drained i ran conected filling loop on boiler and flushed cold through for ten mins.
I have tried turning off all other rads and yes the two downstairs ones do get hotter but once i try and pull heat through other rads tey become cold again.
Reason for fitting two new rads is because previous ones were doubles but single convector and i wanted double convectors because of size of room.
The boiler is a biasi combi 24s and i have 8 rads in total and have aready checked that my boiler can handle it.
All pipework to rads are 15mm so shouldn't really get blocked !!
And i first noticed the problem this winter because i've been using alot of gas and my bill has doubled because room stat hasn't been getting up to temperature so my boiler keeps firing arrrgh!!.
I have not made any alterations to heating prior to this problem arising!!
Hopefully i have covered everything and sorry ifi have bored the crap out of everyone
cheers
stef

 

[corgiman]

IMHO you havent flushed the system right hire a machine

 

[stefbacardi]

I hoped i would get away with just running cold water through and relying on the mains pressure, but your right i'll hire a machine and flush it properly and see what happens!!
many thanks and i'll let you know what the outcome is

cheers

stef

 

[JohnD]

before you spend the money. balance them properly.

This means closing the lockshield, and opening it very slightly, and feeling the pipes. There should be a noticeable drop in temperature across every radiator.

Unless you buy or hire pipe thermometers, the inlet pipe should be "too hot to hold" and the outlet pipe should be "too hot to hold for long"

Your "cold" rads might end up with lockshields opened wider than your "hot" ones as you want to reduce the flow through the hotter ones. Lockshields need to be opened very little.

After you have done them all, go round and feel again and see if any of the outlet pipes are too hot. If so, that means they are stealing extra flow which could usefully be diverted to the colder rads.

What came out when you cleaned and flushed?

Are the rads cold at the top, bottom or middle?

I normally use Sentinel X400 sludge loosener, which I find very good for black sludge. It is non-aggressive and you leave it in for 4 weeks before flushing. Even if this does not cure the problem, it will only cost you £15 and will loosen sediment ready for any further flushing you do.

I am a householder not a pro.

 

[corgiman]

I am only suggesting the machine be used as I dont see that balancing will cure the cold spots at the bottom of the rads

 

[D_Hailsham]

I have changed the order to make it more logical!

I have tried turning off all other rads and yes the two downstairs ones do get hotter but once i try and pull heat through other rads tey become cold again.

When you did this, were the downstairs rad still colder at the bottom? If they were, another flush might help. But if the rads were OK, then all you need to do is balance the system properly.

I flushed the system myself by leaving fernox in for a week as suggested and then opened drain cock down stairs and drained system. Once drained i ran connected filling loop on boiler and flushed cold through for ten mins.

Try using Sentinel X400 and leave it in for about four weeks. After a couple of weeks, shut all rads but one for a time, so the X400 just goes though that one. At the same time give the rad some hefty wallops with a rubber hammer to dislodge any sludge adhering to the inside of the rad. Then shut that rad and do another, until all rads are done.

I balanced the rads by isolating all rad valves first and then opened the nearest first by a quarter/half turn gradually increasing till I got to the furthest rad.

The typical valve is fully open at about one turn from closed. You must remove any TRV heads when you balance the system.

Here is the Balancing Procedure I use:

 

[stefbacardi]

I have borrowed a machine and power flushed my system today and have re-balanced valves as shown by the link that was given to me and it has actually helped thanks

The rads in question are alot more even in temperature now and there are no cold spots now. Its a shame that the pump didn't have any speed settings because even now the flow seems pretty low and it was tricky balancing the rads because i was trying to steal as much flow rate as possible for the downstairs rads.

Many thanks guys for all your help and advice!!
it was much apreciated
cheers
stef