TRV for microbore system - 8mm or 15mm with 8mm reducer?

9 Mar 2008
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United Kingdom
After some more help/opinions please

I'm planning on installing TRVs on all radiators (except bathroom) on a 8mm microbore system.

I've been told that a lot of 8mm TRVs are standard 15mm TRVs with a 8mm reducer in the box. anyone know whether that is the case?

The reason for asking is that the whole CH system (boiler and additional+replacement rads) will be changed at some point in the near-ish future and could be changed to 15mm pipes. Hence if the TRVs were 15mm with a reducer then they would could still be used should the system change to 15mm pipe.

Or should I just buy 8mm TRVs and then replace with 15mm TRVs later if required?

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if you have 8mm now and plan to change to 15mm it would make sense to buy the 15mm size now, they do come with 8mm and 10mm reducers in the box but i have had trouble with some of them sealing possibly if the 8mm pipe is damaged etc, and i tend to use 15mm x 8mm yorkshire reducers for a better job, but even doing this will only involve buying new 15mm olives when you changes the pipes,
PS i don't actually know if you get 8mm TRV's but you won't need them anyway
Some manufacturers make different size TRVs, whereas some just make the 15mm size and include adaptors in the box.

Buying an 8mm TRV now and replacing it in the near future would be a waste of money in my opinion. I'd go for the 15mm TRV with adaptor, personally. I found the 10mm reducing adaptors supplied with Drayton TRV4s work really well, so I would have thought that the 8mm would be similar.

The PTS trade price guide catalogue acts as quite a useful reference guide to what's available in situations like this. You can request one here:
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Thanks for the replies.

I've been having a good look online and most manfucaturers dont state whether their 8mm TRVs are natively 8mm or 15mm with convertors. I've sent a few emails and had a reply from one place saying I'll need to buy the reducers.

This is the model I'm considering (Danfoss RAS C2 with matching lockshield):{7}17

and reducers.

Any comments?

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