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Advice on fitting TRV's to my radiators

Postby schott19 » Thu Dec 04, 2008 4:45 pm

Hi All,

First time poster so hello to everybody in here and really hope you can help.

I have an old back boiler system (with one of those hideous ceramic gas fires on the front :( ) which just has a digital timer unit so im assuming no thermostat other than the one attached to the back boiler (under said hideuous fire).

What i want to do is to put thermostatic radiotaor valves on but i wanted to ask a few questions with regards to this:

1. Is it even a good idea / worth it to put these valves on with having such an old system (i will upgrade to a combi at some point but if it aint broke..)

2. I have seven radiators - do i need 7 valves as in my research i have heard something about leaving one without a trv - but this may not apply to my system - im just not sure to be honest. If i do leave one without - which one?

3. I understand that i need to drain my system to replace all the valves and lock sheilds (most current ones are corroded or leaking a bit) but when i fill it up i read it is good to add an additive to the water - is this true and if so which is best? i saw one called Fernox Alphi-11 but unsure if thats any good.

Really hope a professional out there can help me. Im not a plumber but though id try and have a crack at it myself - just a little stuck / concerned about a few bits and bobs :)

ANy help greatly appreciated,


OH, if it make a difference - i have bought Danfoss C2 15mm (just the one so far to check they will fit)
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Simply Build It

Postby Steve the gas » Fri Dec 05, 2008 6:40 am


1. Yes it is.
2. Leave the batroom or hall rad without one.
3.Use fernox or similar - just put it in small tank in loft when re-filling.

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Postby htg engineer » Sat Dec 06, 2008 12:06 pm

You need to leave at least one without a TRV, this acts as a bypass if all the other rads shut down, as said by StG you would normally leave the bathroom radiator with 2 x lockshield valves fitted as this is the room most people require to be warmest.

Also any room where a room thermostat is fitted - there's no need to fit a TRV.

Adding inhibitor is always a good idea.

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