15mm TRV on 8mm Microbore

9 Jan 2008
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United Kingdom
I am looking to fit new radiators throughout the house which currently has 8mm microbore to the radiator valves. Currently has really old rusty radiators with manual valves etc.

I've decided 15mm TRVs will be best to allow future changing of pipework when a new boiler is installed (hopefully later rather than sooner)

I am planning to use 15 to 8mm reducers for this but should I also be adding a couple of inches of 15mm pipe to the top of the reducer to allow for the fittings of the TRV? I've not yet ordered the radiators and TRVs to tell if this will be necessary but thought I'd check here for the general norm.


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Just use the 15mm to 8mm reducing sets that should be supplied with the TRVs if you've bought ones that will fit 8mm
The raditaor I am after come with valves but they are 15mm. I can always order 8mm ones but will save a fair amount given I have 8 radiators to replace
A word of warning Dave, when it comes to 'thrown in' TRVs, they may not be the best quality in the world!! Unless they're Danfoss, Drayton, Westherm or Myson, you're not getting a bargain but a leaker. So I'd check with the supplier on that one..... ;)

Sometimes there's a lot of unseen damage to the 8mm pipes if they rise through the floor to connect to your existing radiators, bumped with hoovers etc. So it's worth checking for that also. Also, check you don't have Maxitwin double entry type radiator valves.
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I don't have the maxi-twin type valves, just standard manual valves and lockshields. The units dont seem to be branded but they have half decent reviews (screwfix)
Ah I like the look of those reducers, will defintily go with them - Unless anyone has any other suggestions?

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