Some questions about radiator valve on my conventional heating system

[groovybug]

Hello everyone,

I have a conventional boiler with quite old 1970/1980 radiators (see photo). Just a few beginner questions, hope you can help with.


1. The previous owners have somehow managed to lose all the valve cap. How do I figure out which one is the lockshield valve, which one is the original wheel head valve? I imagine I can close the radiator by either valve, but as the system might have been balanced via lockshield, I dont want to mess things up.

2. Is changing the valve to thermostatic a DIY-able job? Most of the guide I have read online is for combi boiler, and advise to get a gas engineer for a conventional system.

3. Without a thermostatic valve, is it possible to control the heat output of a particular radiator but closing down the wheelhead valve slightly?

4. I'm struggle to find replacement wheelhead cap for these. The spindle is the type with two flat sides and two rounded sides (see photo). Do you know where I can get them?

Many thanks for your help!

 

[Mottie]

1. The lockshield valve is normally on the return so heats up last.
2. You’ll probably need to drain the system down first so if you can’t do that, you may need to get someone in.
3. Yes.

4. I’m not a heating engineer!

 

[oldbutnotdead]

1 How foolish of them. Yes either valve will restrict water flow through the rads, get a notebook and work through each valve on each rad counting how many turns it takes to close each valve completely. On non- thermostatic valves it doesn't matter whether the lockshield is on flow or return but installers usually put the control on the flow and lockshield on the return
2 Yes but it's a medium skill level. You'll need to drain down and refill the system, your system has an F & E tank so you'll need to clean that out and isolate it's water supply while you're playing with rads.
3 Yes it is, by closing the valve a bit you reduce the watts per hour that the radiator delivers.
4 Many TRVs come as a pack ( TRV plus lockshield), while you're swapping the control valve you might as well put new lockshields on as well if it's an aged system. So won't need new caps

 

[groovybug]

Thank you @Mottie and @oldbutnotdead . So I guess my remaining question is how to drain a conventional system down properly, step by step if you can. Any pitfalls I should be aware of? Why this is not usually recommended for average DIYer?