How to find flow & return on empty system?

Hi,

I'm in the process of having a new central heating system installed.

The pipework is copper and is drained down at the moment.

I’ve opted for an unvented system. On the advice of the HE, I decided to replace all the rads, as they were 20+ years old, and some were rusting.

I made a note of where the old rad valves were (which side) so I would know which was send and return for the new TRVs (this assumes the people who installed the original system got it right....).

Problem is, the HE has forgotten which way round the pipes went into the old boiler, and he has told me that all new TRVs are bi-directional anyway so it wont matter.

Well, both my towel rail TRVs are unidirectional because I spoke with the manufacturers today.

So, how would I go about finding which pipes are send and return before the TRVs are connected?

I don’t want to ‘try and see’ because the pipework is in copper. If I have to change the valves round at a later date, the pipework will be out and I’ll have to bend the pipes to fit the new valve positions (trv & lockshield valves have different connection distances from the rad). I cant slide the rads along the wall either to acount for the new valve positions because the rads are on hooks (screwfix vertical rads).

I know this is the HEs job, but it’s going to take days for me to figure out if the TRV’s are working correctly, and by then he will be long gone. I doubt very much if he will agree to come back and drain down to change the valves round on the rads for free.


Thanks.

fit new trv's! the majority of the new trv's are bi-dirctional, so as long as ya have a flow and return they'll work ok

If you disconnect each radiator in the system and the boiler then you can do a simple continuity test on one pipe and then mark that as the flow or return and fit the valves accordingly.

Tony

Or blow down one of the pipes with someone at the other end to tell you which one it is coming out of.

I tried the ohm meter, but all the pipes have been earth bonded, so they are all electrically connected.

I asked my neighbour to put here finger over one of the pipes in the garage and let go every 3 seconds while I blew down the pipe from the first floor; oh boy, did this work.

After about 5 seconds of puffing I heard an angry shout from the garage.

Yes, my kind neighbour who had come round to help me in her creme jumper, was now covered in black CH sludge.....

Found the pipe though......

Hope you offered to wipe her down