10 degree difference flow & Return?

[dan_the_plumber]

Not sure if someone can answer me this.

Got called out to bleed rads. When I got there bleed them to find them full of water, no air at all.

Elderly customer complaining that rads not hot at top. However the actual rad is an energy saving low service temp rad, of the type flow and return is just in a loop set inside square fins of about 6" square.

Anyway....The flow pipe is nice and hot. The return is quite alot cooler.

Now abviously the rad looses heat, i mean that's how it works.

But I thought the return was only supposed to be 10" cooler than the flow.

Can anyone suggest the factors which might effect the much lower (I'm guessing 20 degrees) temp of the return pipe please??????????

I loosened the head of the TRV, tested the pin was popping out effectively and I left the head screwed back in loosely

Any help much appreciated....Dan

 

[lame plumber]

sounds like you may have to balance the whole system to get your return temp up

 

[dan_the_plumber]

sounds like you may have to balance the whole system to get your return temp up

Hi yeah thats what I thought.

Problem is these rads are like smart rads (Without the fan)

They only have a TRV on one side with no valve on the other

It only occured to me after I left the property that where the tails enter the rad heat exchanger there may be two ballafix.

As far as I can tell the only way of balancing the system would be to use these ballafix.

I don't fancy my chances, especially seeing as there are around 30 radiators!

I'm not sure if i'm looking at this problem the right way, do you think there could be anything else or any other way i may be overlooking?

I think we should bare in mind that the flow is piping hot!

Read more: http://www.ukplumbersforums.co.uk/c...ree-difference-flow-return.html#ixzz2DognSf7C

Cheers....Dan

 

[dan_the_plumber]

I think we should bare in mind that the flow is piping hot!

 

[tamz]

Depends on the system. Pump pressure and valve settings effect the temperature difference.
Condensers should be set up for a 20º drop.

 

[dan_the_plumber]

Depends on the system. Pump pressure and valve settings effect the temperature difference.
Condensers should be set up for a 20º drop.

Ok yeah maybe i'll think about increasing the pump speed then

Cheers....Dan

 

[johnnyplumb]

is the pump powerful enough ?
if there's ballofix valves on rad tails, open them up fully [ you can balance rads later ]

turn the pump speed up to max, with the speed on max, if the temp difference is still greater than it should be, you may need a bigger pump.

 

[SimonJohns]

High flow temp and low rerun temp can happen at low flow

You should be looking for 20-30 diff on start up.

If you have any greater than that there are two explianations

1. It's a combi and its just changed over from hot water and you do get a bolt of boiling water

2. Poor circulation. Water is staying in the hex too long. Check that the balance is correct and that the lockshield a are open enough. Is there sludge in the system preventing flow.

 

[dan_the_plumber]

High flow temp and low rerun temp can happen at low flow

You should be looking for 20-30 diff on start up.

If you have any greater than that there are two explianations

1. It's a combi and its just changed over from hot water and you do get a bolt of boiling water

2. Poor circulation. Water is staying in the hex too long. Check that the balance is correct and that the lockshield a are open enough. Is there sludge in the system preventing flow.

I think it's a system boiler serving the CH and there's a gas fired invented cylinder for DHW.
There are no lock shields on the system only balls fix in the rads.
Could be sludge but I don't think there would be much.
Im thinking that maybe the boiler is just not big enough.
Not sure the heat input of boiler, but there are prob 30 rads in the care home.
Heating never goes off, runs constantly to keep the old folk warm

Dan

 

[blade11]

as already stated 20 degree difference on condensers alls well.

 

[SimonJohns]

Wow. Ok

Big system

Sounds to me like boiler over rated and pump too small

 

[tamz]

If it is a care home the system has been designed to prevent high temperatures on the rads to prevent burning.
Don't play with it.

 

[AWheating]

room temp ok?