CH/Boiler flushing

[robgul]

Quick question here as I've not had any reply on the plumbing forum I follow . .

I have the system drained down at the moment to fit a couple of electric elements to towel rails for "dual heat" - CH in the winter, electric on timers in the summer.    I'm wondering if before I refill the system whether it's worth (or would be effective) to flush the system out (it's a boiler + HW tank pressurised system, not a combi)  -plan would be to leave the drain cock open with the hose in a drain, close all rad air vents and open the supply/re-pressure valves to let new water in . . .   and let the water run through and out for a bit . . .  before adding inhibitor and refilling/bleeding the system.

It's not a "power flush" but would it work/is it worth it?    The towel rails had quite a bit of black dust in them when I took them off the wall (and then flushed them with a hose outside)

[Kim]

Last time I had reason to drain a heating system I did just that, on the principle that sludge was better out than in.  You can get a bit more sludge out by manipulating the radiator valves.  No doubt the majority of it remains undisturbed.

[Canardly]

I would say yes.

[Von Broad]

I ain't no plumber/heating engineer.....so be warned

but if I was doing this ...
I'd close off the the flow and return to the boiler  to keep as much crap out of there as you can, then I'd shut all the flow and return valves on all the radiator, then I'd work on one rad at a time opening each one a
as you go, and subsequently closing before moving on to the next one.
The reason for doing this is, depending on how your system is balanced [and many are not] if you leave all the rads open and you start flushing, water will always find the path of least resistance and so you won't really know whether you're getting an even  'flush flow' round all the rads depending on how the system has been balanced. Such a process won't guarantee  that sludge will be removed, but you start more of a chance of it doing so.

Then when you fill up.....you can balance the system properly!!

[robgul]

I ain't no plumber/heating engineer.....so be warned

but if I was doing this ...
I'd close off the the flow and return to the boiler  to keep as much crap out of there as you can, then I'd shut all the flow and return valves on all the radiator, then I'd work on one rad at a time opening each one a
as you go, and subsequently closing before moving on to the next one.
The reason for doing this is, depending on how your system is balanced [and many are not] if you leave all the rads open and you start flushing, water will always find the path of least resistance and so you won't really know whether you're getting an even  'flush flow' round all the rads depending on how the system has been balanced. Such a process won't guarantee  that sludge will be removed, but you start more of a chance of it doing so.

Then when you fill up.....you can balance the system properly!!

Whilst having my lunch, since starting the thread, it did dawn on me that pushing crap into/through the boiler may not be a good idea- and that I'd have to fiddle with the rad valves.

The (one) CH circuit is badly planned with it running round the house at first floor level - thus all the ground floor rads "hang" from above for their flows and returns . .  and none of the ground floor rads have drain cocks  - who designed that?  I did fit an extra rad downstairs last year and had to drain the rad I was teeing off the hard way, cracking a valve and using a bowl that had to be emptied n times.   In the medium term plan is to remedy the issue and fit drain cocks to the downstairs rads . . .  which would enable me to take them outside and flush with a hose.

For the moment I think I'll just stick the inhibitor in and refill the system.   

The electric elements were pretty simple to fit to the towel rails with a T-piece that the existing valve locates to with a short diversion of the 15mm pipe.  Each one is wired to an unswitched, fused spur with LED fed through a length of trunking in the corner of the bathroom to a couple of Hive time switch/sockets located in the loft.  They'll be programmed to come on for just enough time to dry post-shower/bath towels in the morning and late at night.