CH circuit flushing help please

[SparkyTris]

Planning to use Fernox restorer then inhibitor in my CH system which is of the open vented variety. Property is a top floor flat, with microbore pipes running underfloor to rads. I have a pump on the output side of the boiler.
How best to "flush" the system until water runs clear, as per directions on the bottle?

Presumably I will have to open a rad union and collect the water there during the flush, but this will never completely empty the circuit because of the underfloor pipes?

do I need a powerflushing unit? what is a powerflushing unit? can I just run the pump to give me a "powerflush"?

 

[kevplumb]

for what will be left in the pipes drain /refill
run the system 10 mins
drain/refill should get it out
then add your cleaner
same again when you add inhibitor
theres a couple of posts down the page as well

 

[SparkyTris]

OK, Kev thanks for that. Have read the other posts. Think if I understand correct that if in doubt, just flush through from the F&E tank.

Do I gain anything by re-using the water that comes out to begin with - I sloshed in a carton of inhibitor last year, so the stuff that's in the system at the mo has some inhibitor in it, but more importantly, it's stale water and won't have as much dissolved gas as fresh mains (?)

I had this zany idea that I'd let the original coolant stand for a while, let the cack drop out of it then rack off the clear and put it back in when I re-fill the system after cleaning. am I barking?

 

[kevplumb]

i suppose you could but is it worth the bother

 

[SparkyTris]

I've no idea if it would give any advantage, how much of a problem is corrosion in microbore CH circuits? I just thought, if I've got a circuitfull of "flat" water, it would be kind of a shame to waste it in favour of fresh that's virtually guaranteed to be more gassy and corrosive ? the system is relatively new, I guess 10 years or so. The current coolant is 12 months old, and had 4l of protector added then

 

[kevplumb]

no just refill and add the inhibitor
corrosion aint the problem with m/bore scale/ sludge is

 

[ChrisR]

Letting water dribble out of a rad union isn't "flushing"!

Take a rad off and you can connect hose(s) to the valves with garden tap connectors. Might need a couple of washing machine hose washers to be leak-tight. Put a push-fit cap on the vent in the loft, and put a full flow valve on the feed. Afterwards leave that open with the handle removed.

Then you can connect the mains to one of your rad valve unions and it will come out of the other one. Open one rad at a time. Best if you have a valve to stop flow through the boiler to put more flow through rad.

Don't worry about the amount of oxygen in one fill of mains water. It isn't enough to do anything if you put inhibitor in.

A power flusher would be less pressure than the mains, but rapid reverslaof the flow direction is what you really need to get the grot in radiator bottoms up into suspension.

A better place to connect is at the pump unions, though you'd have to get some fittings together to be able to connect. Less than £10 worth.

 

[SparkyTris]

Chris, thanks a lot for that. What's a full flow valve? presumably this is also to stop the mains pressure flush from filling up the F&E tank?
thanks for dispelling my gaseous fears.

 

[kevplumb]

full flow valve has no restriction to flow ie gate valve

 

[SparkyTris]

Right. But for the flushing procedure, when I have mains connected up down below, I should keep the gatevalve shut right?

 

[kevplumb]

would think so or you will get wet