Flushing combi CH system via the filling loop

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Evening all

I have read the following excellent post:

//www.diynot.com/forums/viewtopic.php?t=38902

which details how to flush a system using the filling loop. I thought I'd give this a go this evening.

Two things to mention first of all:
The four-radiator combi boiler heating system works fine. All radiators get hot within a reasonable amount of time and the heat is spread evenly from top to bottom.
I didn't drain the radiators before starting (wasn't sure of the best way)

I wanted to try this in order to replace the inhibitor (F1) containing water in the system with fresh water before adding some F3 and running it for a week (as per the instructions) before my new boiler is installed.

The filling loop on my boiler goes into the flow pipework. Things I've read suggest it normally goes to the return but that it doesn't really matter.
On one of the radiator's return pipes there is a tap with a spigot for a hose. Presumably this was originally put in to facilitate draining of the system?

I closed off the flow valve on the boiler, hooked up a hose to the drain valve, opened it and then slowly turned on the filling loop. The pressure on the boiler built up until it was sitting at about 2.5 bar and steady. I went into the bathroom expecting to see a torrent of water flowing out from the other end of the weighed down hosepipe. A trickle! A very slow trickle:

(check out the exciting video)

I then started to close off the radiators (both valves, non TRVs) until I had one remaining fully open. The flow of water did not increase whatsoever. I left the water flowing until I had just over one full bucket and then checked the temperature of the radiator. The bottom was very cold (the temperature of the incoming mains water) but the top was still fairly warm from where the heating had been on an hour or two before. I then opened up the next radiator, closed the previous one and did the same thing.

From reading the instructions, I am guessing that I should be getting more flow through the hosepipe?

Any suggestions? I'm hoping I've put enough clean water in so that the F3 can work as intended. I'll be flushing it out again this weekend, so I guess we'll see if there's any improvement in the flow.

All of the water that has come out so far has been perfectly clear. Now, either I'm very lucky and my 30 year old heating system is in perfect order, or something's not quite right...

Suggestions and comments greatly appreciated.
Thanks
 
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Take the hose off and see whats coming out of the drain off. If its flying out check hose for blockages. You would probably be better off just draining down, refill, run it round for a while, drain again then add f3 and refill.
 
I must admit that I flush mine in a 'dilution flush' by the filling loop as my CH system is fairly sprawling and difficult to get all the air / water from (depending on filling or draining).

I use a cheap TDS meter to check the flush is complete, and my incoming mains is at 1.75bar. I'm not on a water meter.

Probably works better than a fill / draindown / rinse for my system.

I suspect that the drain cock washer is stuck to the seat and the water's only coming out the hole in the middle.
 
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thank you both for the advice. It was indeed the washer stuck to the drain cock seat. I fished it out, fitted a new one and greased the threaded mechanism. It now works a treat.
New boiler install almost finished and the water that has come out of the system so far has been pretty clear.
While the system was empty I thought I'd kill two birds with one stone and fit a larger double panel radiator in the bathroom with a TRV. It's been a DIY-filled weekend, the pro working on the boiler and me the amateur getting smaller odds and sods done like the condensate waste run and bathroom radiator.

My first attempt at solder ring pipework seems to have been a success. The real test will be when the system is pressurised.... Fingers crossed.

Thanks again!
 

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