Installing TRV's on 10mm microbore

2 Oct 2009
Reaction score
United Kingdom
I have a 10mm microbore open vented Central Heating system with has traditional valves on all the radiators, I am looking to replace them all (except the one on the radiator in the hall where the thermostat for the system is located) with TRV's from Toolstation

The TRV's state that they are 15mm with a 10mm reducer so my question is does this reducer do away with the need for a 10mm olive? The current valves are 10mm so I plan to remove the valve and carefully cut off the exising olive and then fit the 15mm-10mm reducer and new TRV, will I have any problems with leaks from where the old olive was fitted as I do not want to have to replace pipework if I can help it? :)
Sponsored Links
Plumb centre bulldog range come in proper 10mm size
Sponsored Links
No need to change tail into rad if its the same
There 2 tail types; 1/2" and 3/4". This refers to the nut between the rad and the valve. Most, if not all, TRVs are 1/2" whereas many standard velves are 3/4".

A picture of your current valves would help to clarify what you've got.
Screwfix do a siemens trv (10mm adapter included), i've fitted 9 of these over the last 3 years. No problems as yet.
Since the 10 mm tube is soft, in most cases the nut has been over tightened and the olive needs to be cut to remove.

So in most cases its necessary to solder a new length of 10 mm tube.

But in most cases its easier to use a 10 mm to 15 mm adapter and use standard 15 mm valves with a short length of 15 mm tube.

Tony Glazier
Thanks all I have opted for the Bulldog 2 TRV's for the system from Plumb Center which are a 10mm without reducer connection and are the same (Plumb Center own branded) as the Pegler Terrier II TRV's that screwfix sell at £5 more per valve!!

I will post once they are all fitted and working but one last piece of advice would anyone PTFE around the new olive as well as the thread of the valve body?
I don't see how you are going to get the old olive off without damaging the pipe.

But if you don't use PTFE on the new olive its very likely to leak.

The next door but one neighbour (who is a relative) has done his with a very gentle junior hackscrew. Was speaking to him last night and he swapped 11 valves without a leak or squashed pipe.

Here's hoping!!!! :unsure:
No need to change tail into rad if its the same

Fitting the Bulldog 2 TRV's yesterday to 9 rad's and I had a result in that they fitted using the existing nut and olive to both the pipe and rad and not a dropped leaked.

The TRV's are working a treat and for the money I can highly recommend them.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links