2 new rads in old system - not working

[favemuppet]

Have looked for a similar problem on this site but cannot find, so apologies if dealt with elsewhere!

Moved into new house - built 1960s. CH system (combi boiler only year and a half old) has big old rads and big steel pipes. 2 extensions were built last year by previous owner and these 2 rooms have new slimmer rads and thin copper pipes.

Problem I have is that these 2 new rads do not get hot. Plumber I know tried to balance the rads but no joy. He said that cos the old pipes were bigger the water was tempted to flow to these first so the new pipes would struggle. I do note that its not only the rad that stays cold but also the upright copper pipes.

He also suggested system needs flushing through as water in one of the new rads was black (which for some reason he couldnt do).

Does this sound plausible?? Is there actually another fault here? Or do I resign myself to a complete overhaul of the CH system?

 

[corgiman]

more than plausible if the rads used to work.

 

[favemuppet]

Plumber did get the new rads working for a bit, but they go cold again after a day or so.

 

[bengasman]

Sounds rather odd to me, that story about the bigger pipes. The flow per radiator is squeezed to need with the lock shield valve, which makes it pretty irrelevant whether the flow and return pipe are 2 inch or 15 mm. My money says some muppet linked the flow and return pipe to form a loop. That may have been useful on full gravity systems like they had in my grandfather’s days, but today you need to have the flow and return NOT connected. Simple test to find out. Turn the heating off and wait til cold. shut off ALL rads. Set the boiler at medium hot. Turn heating on and feel flow and return pipe, preferably a bit away from the boiler but BEFORE the first tee. The boiler should start cycling and the pipes should stay cold, if they get hot, you follow the hot pipe, find the connection and cut it. don’t forget to cap of the two ends

 

[favemuppet]

On both rads the flow pipe (is this the end with the lockshield valve?) is warm but the return pipe is cold. What does this suggest?

 

[ChrisR]

I think what the muppet probably did was connect the 2 new rads directly across one of the old ones, so as soon as that old rad is open it kills the pressure available for the new loop of "thin" pipes. How thin are they? 15mm?

To test, turn off all the rads it's likely to be, and see if your new rads get hot.

Of course if he's a double plus star extra woolly muppet, he'll have connected both ends of the two new rads to the flow and none to the return.

 

[dal5band]

Means there is flow but not enoug - probably air or some obstruction.

- Gradually turn down the other rads starting with the ones nearest the boiler.
- May need to go as far as turning off a lot of the other radiators completly to force the flow through the new radiators - this will clear any air or other obstruction, then you can turn the others on.
- turn the pump to max for a few days to get the flow established then turn it down to what it was.

 

[Nige F]

house - built 1960s. CH system big old rads and big steel pipes. 2 extensions were built last year by previous owner and these 2 rooms have new slimmer rads and thin copper pipes.

resign myself to a complete overhaul of the CH system?

Big rads, steel pipes ....one pipe system new rads connected by Corgi

 

[Timmyturtle]

Just what i was thinking..one pipe system

Turn off all the rads except the cold ones

If they become hot then its a flow problem

This will either be sludge or just the need to properly balance the heating circuits

I know its silly but make sure the valves are open on both sides of the cold rads

 

[Timmyturtle]

Just a thought if its sludge...
Wouldnt recommend a powerflush on old steel pipes,had problems there.

 

[favemuppet]

Just a thought if its sludge...
Wouldnt recommend a powerflush on old steel pipes,had problems there.

What problems?

I have been told elsewhere that power flushing would not necessarily cause a problem.

 

[bruce 1411]

powerflush may not cause problems but consider this if you have sludge blocking corrosion pin holes in the pipes taking it away with a power flush will let the leaks out i did my entire system by hand one rad at a time