How to drain rads on combi system?

[mark121]

Hi,

I'm looking to install TRVs and replace a couple of rads on a system heated by a combi boiler. Looking at other references on the web for draining rads they all advise to bring someone in if on combi or closed system. Not sure if I'm missing something obvious but wanted to know why the procedure is so different, i.e why should I not drain the rads myself after ensuring the boiler is off and re-fill when work is done?

Also struggling to find a low point drain. Have checked all rads and exposed pipework that I can find but not found a drain point. Any advice on how best to complete without leaking gallons?

Thank you in advance,

Mark

 

[JohnD]

If you are draining down and fitting TRVs I would take the opportunity to fit some Lockshield Valves with drain-off at the same time.

They are very convenient. If you have solid ground floors with the pipes running down from the ceiling to the rads they are essential.

If you have no drain-offs you can (this time) probably find a garden hose connector or a washing machine hose that will fit onto your rad valves. You will have a bit of leakage while you fit it, though.

Unless you know for a fact that the system is very clean, quite new and has had inhibitor from new, I would also give it a chemical clean, flush and refill with inhibitor while you are working on it.

If black sludge falls out of the rads when you take the old valves off, take them outside and run a garden hose through them as well. It will shorten the life of your pump and may cause blockages.