Flow and return configuration

[Chief777]

Morning all, I'm new here so hello and HNY!

Moved into a new (1930's) house before Christmas. The rear extension is cold compared to the rest of the house.

In the extension there are 2 plinth rads and 1 standard rad, all fed from a single flow and return loop. Issue is they are connected in parallel. Should they not be connected in series?
Being connected in parallel on a single flow and return loop leads me to suspect the return loop is being interrupted with the output from each of the 3 rads which is mixing the flow & return loop and therefore preventing a decent flow of hot water through furthest rad 3.

Thanks,
Chief.

 

[Madrab]

In a standard 2 pipe configuration all rads are in parallel. That way the system can feed all the radiators without any interruption to the flow and return. If they were pipe'd in series as your diagram suggested, if one radiator closed down - say when the TRV closes, the other radiators further down that line wouldn't get any flow. Bit like the old fairy lights, if one went out it would kill the rest as it would break the circuit

The way a normal 2 pipe system works is there is a separate flow and return backbone, usually 22mm, each radiator's feed then branches off the main flow pipe (which will end at the last rad), the main return pipe then starts at that last rad and runs back to the boiler, with each radiator's return branching into that return.

Your main problem, by the sounds of it, could be a balancing issue, correct balancing ensuring each heater obtains enough hot water flow to heat it up, (search balancing on here and you will find a walkthrough) either that or either the valves aren't working properly or the heaters are sludged up/blocked.

 

[fixitflav]

Issue is they are connected in parallel. Should they not be connected in series?

No, they should be in parallel. But I don't understand your sketch, with a pipe coming out of rad 2.
If the rads in the extension are getting hot, but the room isn't warm, could be they're undersized. If they're not getting hot, but other rads are, need balancing (as Madrab says). Throttle down some of the other rads.

 

[Madrab]

Yup, as suggested, shut down all the other rads and see if these ones get hot, if so then it's a balancing issue.

 

[Chief777]

Thanks all, makes sense that they are in parallel.

The 3rd rad is the last to get hot so I will balance the system as you describe. I'm pretty confident the system is clean and the reason the 3rd rad is last to heat is it's, I suspect, furthest in the system....being in the extension.

Fixitflav, mistake in my sketch...well spotted.

 

[oldbuffer]

1. What size (outside diameter) are the flow and return pipes?
2. What are the heat requirements of the radiators? Probably marked on the plinth heaters. Please give height, width and number of finned surfaces for radiator.
There is a limit to the amount of heat pipework can "carry". It has been known for builders to extend a heating system without calculating the correct pipe sizes.