How many RADS are in a single pipe system?

There are 7 rads: the first is inline with everything (directly after the boiler output) and is properly hot, and then it splits into one single-pipe system for upstairs (2 more rads) and one single-pipe for downstairs (4 rads). All 6 rads on the one-pipe systems are inadequately hot.

Is the return pipe from each Rad hot or cold?

The feed pipe to every rad is very hot. The return pipe from each rad is cold. However the rads themselves are only warm-ish at the top, cold at the bottom. House doesn’t get warm, even with heating full on. I don’t think it’s a balancing issue: upstairs is as cold as downstairs. What’s going on, and what can I do to improve the situation?

Do you have a single pipe heating system?

We have a single-pipe heating system. Several rads are new and have new valves (not TRV, just normal ones), all of which are completely open. All rads have bypasses under them. Pipe leaving the boiler is very hot. Pipe returning to boiler is almost as hot. The feed pipe to every rad is very hot. The return pipe from each rad is cold.

Do you need a TRV for a one pipe system?

One pipe systems need special low resistance trvs as the radiators actually heat by gravity (thermosyphon is the new word for gravity). Std trvs will not work unless the main loop is directly below the rad and even then the rad will not heat properly.

Can you use radiator on one pipe ch syestem?

No mate, you’re relying on convection to feed the rads on a one pipe. Seeing as this is the last rad there won’t be much of that cos the water will be a lot cooler. The only things I could suggest is to use swept tees and bends instead of elbows if poss. And turn the other rads down of course.