Flow and return issues

Access Gas · May 11, 2015

Hi guys,

Ive been registered on here for a while and never really used the service but it looks like many minds are better than 1.

I have a property with 6 rads and 1 cylinder s plan system boiler the upstairs rads have issues.

Nannys room - TRV shut off the return pipe gets hot, when the TRV is opened the flow pipe gets hot fast and the rad heats up, the return pipe goes cold but doesn't warm up

I do expect the return to be colder than the flow but the difference in temperature is more than 20 degrees.

Kids room has the same issue with temperature difference and sometimes doesn't even come on at all.

Main bedroom has same issue with flow and return temperature difference but not all the time, somedays the difference is only 5-10 degrees after being on for 10 minutes.

I have vented the flow and return pipes individually thinking there are air locks as the nannys room radiator collects a lot of gas.

I have suggested a powerflush but in all honesty I don't think that Is the problem.
What is confusing me is why the return pipe in the nannys room gets hot when the rad is turned off, if there was letby to the TRV surely the flow pipe would be getting hot.?

it seems like there is a flow coming through both pipes but one has more force than the other. In my mind if a flow pipe is connected to the return surely it will just go back to the boiler like a bypass valve.

Hope someone can give some advice-

thanks in advance

Tan

Best · May 11, 2015

Return pipe can heat up a bit if the main return pipe it is linked to is fairly close by & the pipe to the rad is all level, or slightly rising. The pump cannot pump that direction, but heat rises by gravity
As to your problem of temperature difference between the flow & return at rads, - on a condensing boiler it is supposed to be 20 degrees difference. But you might have a problem with the circulating pump. Pumps can fail a bit & not heat the furthest, hardest to pump around rads fully. That's if you don't have crud in the pump, or valves or a pipe.

Access Gas · May 11, 2015

do you know why the return pipes wont heat up to a descent temperature? even after an hour or so they are just 20 - 30 degrees while the flow pipes are 60 - 70

The downstairs rads all heat up instantly with both flow and returns similar temperatures, I have even balanced the system

Best · May 11, 2015

Slow poor flow through them. Could be anything causing that, on either pipe. Don't be fooled by flows to rads being hot at valves, - will still be hot with reduced flow until water gets into rads.
I would check for obvious things - like system pressure, dirt in rads, pipes or circulating pump etc. Check motorised valve is working ok & not blocked.
You could perhaps try running water through a hose from an open rad valve on each side of a rad that isn't working well, Then I would consider replacing circulating pump. It is less likely to have much dirt in a system that has always been a sealed type.
If you try turning all the other rads off, do the offending rads work better?

Access Gas · May 11, 2015

I haven't tried turning them all off, customer says the boiler is only 1 year old and doesn't know if they powerflushed the system, but apparently shes been having issues with the upstairs rads from when she moved in 2 years ago

Best · May 11, 2015

At least you are not responsible for the original install. You never know what somebody has done with the pipework. The cylinder pipes will rob the flow from the rest of heating if hot water heated at same time & unbalanced to coil.
What I am wondering is, why is there air gathering if it is a system boiler? Sealed system shouldn't have air unless it is due to corrosion gases due to it originally being a rotten system.
I have come across a few where it was just a wee blockage somewhere in a pipe. Also had one where a motorised valve was seized just slightly open.
Hope there is no hidden valves somewhere, like these stupid isolating valves idiots use?
Circulating pumps I don't rule out.
Bypass valve at boiler should be set properly or it will derate the performance of the pump.