Draining down coz non-working CH rad. Re-use the same water?

12 Nov 2009
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United Kingdom

Householder here. Non-expert.

Central heating circulation.

One of my (total three) radiators doesn't get hot.

It is full of water (no air).

There is a regular lockshield value at one end and a TRV at the other. They are both open. I have checked the spindle in the TRV (FAQ6). The system pressure is 1.0 Bar (in the green zone).

I had tenants in for a while and when I returned the lockshield valve had been turned-off. I am wondering if some sludge has settled and blocked something up.

Also tried:
Balancing. FAQ5
Turned off the other radiators. FAQ21
(I have read the wiki about DIY-mains flushing, but that all seems a bit scary and above my pay-grade).

Before I shell out for a powerflush, I thought I'd drain-down the system and, err, dunno, poke some pipecleaners through the valves or something, (?rod out a few pipes, remove the radiator and manually flush it through?) to see if that helps.

My question is, is there any point in keeping the old water in bottles and adding it back into the system when I come to refill it (rather than filling it with fresh water from the mains)? That is, to prevent adding in more calcium/magnesium salts that will add fur/limescale when heated. I would leave any crud/solids to settle-out before re-adding it and also add some inhibitor.

Boiler is a WB Greenstar i ErP combi with a Greenstar System filter. Closed system. It has a filling loop. Hard water area.

any help appreciated

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Remove the radiator and see if water flows continuously under pressure from both valves. A second person topping up pressure at the filling loop whilst you work the valves. No point in trying to re use the water lost whilst doing the above. Tell us the result.
Whilst rad is removed ,flush it through.
It'll take ages. Why not do what you have to do, fill with fresh to test it's all working and if okay, drain out enough to be able to get a litre of inhibitor in? In fact, with just three rads, I'd take 'em all off and give them a good flush through outside. Could it just be a faulty/blocked valve?
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You say you have tested the TRV but how exactly did you test it
...I just took the cosmetic-top/dial off the TRV and bounced the brass needle up and down a few times. It was nice and springy and didn't appear to be stuck down...
Do as @terryplumb says #2, or close the Lockshield and TRV, open the bleed valve till no more water comes out into a dish, then open each valve one at a time to see if water starts to come out with each valve open one at a time, if it doesnt that valve is your problem
Do either of the pipes get warm/hot? I take it that it worked previously? If you suspect sludge, why would you re-use the water? (n)
Do either of the pipes get warm/hot

I take it that it worked previously?

If you suspect sludge, why would you re-use the water? (n)
Only because the calcium carbonate/limescale etc has already been 'boiled' out of it already.
I would let the sludge settle-out first (or coffee-filter it out). I wouldn't pour the sludge back in!

There are now strong indications it is a broken/stuck TRV.

I ended up draining-down the whole system. (I was planning-on just draining down the affected rad, per#2, but forgot to close the valves first(!)).

The flow/lockshield valve flows OK.

I took off the TRV entirely and it doesn't allow water though it when pushed up against a regular tap. I have a spare TRV kicking around and that one (same model) does. (Both are marked as the 'two-way-street' type).

I'll refill it all tomorrow. I have 1 litre of Sentinel X100, which says it is good for systems upto 100 litres. My system only gave up about 20 litres, so should I just use 200ml of Inhibitor, or bump it up to 500ml; or the full 1 litre?

I still have the old water in bottles, I could reuse!! Drained through the nuts at the bottom of the affected radiator. It is clear as a crystal lake (well, one that has been peed in). I haven't flushed the radiator, I guess that there is no need.

Presumably, it's OK to leave it all empty overnight? (e.g. rust-wise)

Best to fit the valves and close them if not connected to a rad.... Not wise to leave open ended pipes.
500 ml of inhibitor is plenty.
Thanks. Yeah, it's all already fully bolted back together, just awaiting the water, which I'll do in daylight...

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