Fitting TRV`s on microbore

[Andy]

Hi,

I am looking to replace the standard microbore radiator valves with trv`s. How easy an operation is this? And what sort of precautions should I take?

Thanks

Andy

[Andy Hall]

It's quite easy.

Are these the type with both pipes at one end or one pipe at each?

AFAIK, you can't get TRVs with the both pipes at one end configuration, so if you have this, you would need to add a length of pipe run behind the radiator to take the second pipe to the opposite end.

If this kind of work is needed, you will need to equip yourself with solder fittings, tube and a hand pipe bender (cost about £10-15).

Otherwise, the procedure is to drain down the system and empth at each radiator. TAKE CARE because heating water typically contains dissolved iron salts and possibly sludge and this will indellibly dye carpets and decorations. I use plastic cat litter trays from the supermarket placed under each end of a radiator. You need plastic sheets, newspaper, perhaps old towels etc. in case.

If it looks like the system is sludged, this is a good opportunity to remove the radiators and hose them through outside. For this, disconnect the valve unions and put a small plastic sandwich bag on the tails fastened with rubber bands. This avoids drips on the floor. Afterwards you can remove the tails. If the system appears sludged, it's worth flushing a little water out of each valve as you go.

You can get microbore TRVs and many are 10mm size and come with a reducer set for 8mm. I'm not enthusiastic about reducer sets because they do have a tendency to leak. In general I prefer to get standard 15mm TRVs and use a microbore female socket to 15mm pipe tail adaptor. The microbore solders into the fitting and then you can push it into the TRV as though you had 15mm tube. I always use Invensys TRV4 valves, mainly because I've done so for about 25 years and have had good reliability with them.

It's also worth changing the lockshield valves unless they are fairly new. I used Pegler Terrier valves last time and they are also pretty good. They make one with a drain c*ck in the tail. This gives you a drain point at each radiator and means that you can remove one radiator at a time for decorating.

For the valve tails wrap about 6 turns of PTFE tape around the tail in a clockwise direction as you look at the end of the fitting that will go in the radiator.

Afterwards its worth running the system with some cleaning and flushing agent according to the maker's directions. THen flush with clean water and add inhibitor.

[Simon Hawthorne]

I asked the same question a few weeks ago, and have successfully finished only one rad so far (10 to go!). I have 8mm - and the rads had flow and return valve on the same side.

Follow Andy's instructions and you won't go far wrong - especially the bit above about the multiple wraps of PTFE tape. I didn't first time and this was the only leak I had (I used compression joints until my soldering improves!).

Si