I stupidly forgot to label the flow and return pipe before my floor screed went down in my new extension. System was partially in use so I drained and thought I’d correctly identified the return by slowly adding water to the system (fill is attached to the return side) until water came out of one of the pipes new pipes having taken all the end caps off.

Radiators all on, lovely jubly, the entire house is warm… finally!

Except…. It seems like some how I’ve got it wrong identifying the returns as I’ve now got my lockshields on the warmer pipes attached to the rads (ie the flow side).

So, I understand that a tiny air bubble in a mostly closed lock shield could in theory stop the flow. Does this really happen?

My TRVs (Drayton TRV4) say that they should be installed vertically on the flow side, or horizontally on the return side, indicating that the valve that shuts off the water flow is designed to work in one direction.

My TRVs are definitely doing their job despite being on the “wrong” side. Should I worry about this or do the job properly and drain the system and swap them all round?

thanks in advance for any advice.

If you want them to work efficiently and as per the manufacturer’s instructions, you know what you need to do. It’s not such a tricky job – half a day. Just do it!

I know that’s the right answer. Damn it.

I’m also not really sure how I incorrectly identified the returns in the first place. With the whole system off, no water could go through the 2 zone valves so it must have come out of the return pipes surely?
The evidence of temperature differential is pretty clear now though.

I thought I read that nowadays it doesnt matter which way round the TRV is on the Rad – in older ones you used to get a knocking if fitted to the return side inadvertently.

For good order I fitted all mine to the flow side though. Lots of scribbles on the floor boards 😉

further googling indicates that most people say that the TRV4 is bi-directional. I think it’s just the instructions on the box are a little confusing / out dated.

stoner speaks the truth

It really doesn’t matter in practice, don’t bother.