Central heating Rad-Stem Elbow change Guidance Please

5 Jan 2007
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United Kingdom
Hi Everyone
a very happy and healthy new year to you all.

i need some help/guidance on how to replace an old stem elbow on a radiator. i have changed radiator valves a few times with no problems but i have never replaced a stem elbow and nut on a rad before. please see the picture below.

i believe i need the stem elbow on the link below which will go straight into the 10mm pipe (replacing yellow elbow) with an insert? i think that bit is straight forward but please correct me if am wrong.


Now where i need help is how to connect the other smaller end of the stem elbow to the TRV valve. i believe i need some sort of compression reducing valve set which will have the necessary 10mm olives and other bits i will need?
can you please guide me on how this is done and any links to buy the necessary parts. i have been searching online (screwfix/toolstation) but i dont want to buy the wrong bits.

i have searched youtube but annoyingly cant find any videos on this sort of job. a lot of videos on replacing valves etc but not on this sort of job.

are there ready made full sets of stem elbow with the nuts/compression set that i can buy please? cant find any online.

any help much appreciated

thank you all and HNY...


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Is there a reducer on the inlet port to the valve ? If the inlet port of the valve is 15 mm then a stem elbow 10mm to 15 mm stem would only require a 15 mm olive.
thanks for the quick reply Terryplumb. i havent taken it apart yet so not sure about reducer. sorry if am sounding silly. shows my level of ignorance with this.
looking at the picture i posted, i susptect there must be some sort of reducer within the nut (circled with blue)below the valve? reducer will convert the 10mm male elbow end to fit to bottom of valve? these are the bits i have no clue on. thank you


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There may well be a reducer ,most inlet ports on TRV's are 15 mm. I can't ever remember seeing a TRV with 10 mm inlet port ,seen wheel heads and lockshields but not TRV.
But why you would want to use a reducer set ,when you can buy stem elbow with 15 mm male end beats me !!
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But why you would want to use a reducer set ,when you can buy stem elbow with 15 mm male end beats me

15mm stem elbow wont fit pipe side, as pipe is 10mm?

i believe the elbows are either 10mm-10mm or 15-15mm, right?
You need a 10 to 15 stem elbow.
10 mm female for pipe to go in and 15 mm male to go into valve.
ah thanks . didnt realise 10mm female-15mm male elbow existed.

ok so i will need an olive and insert for the 15mm side, correct?
I think the stem elbow comes with a stiffener fitted , and you would need 15 mm olive . The 10mm plastic pipe should already have a stiffener fitted ,but check it anyway !!!
Are you fitting a new TRV ? The existing ones nut will accommodate a 15 mm olive.

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