DIY powerflush - rads stay cold during flush with warm water

[alban]

Trad open-vented system 20+ yrs old with Netaheat 16/22.
In process of P/Flushing - when flushing any individual rad with others turned off only the bottom line between the therm and lock/s valves warms up if at all but not main body as per instructions. Funny thing is that the rads when used normally heat up reasonably, tho' slowly and a bit cool along the bottom. D/stairs rads are fed from drop down pipes from ceiling. Makes me think summat ain't right.

Point of flushing was to try to desludge boiler heat exchanger as it seems to overheat and shut down on any setting above Min.

Disappointing amount of sludge removed by P/Flushing with chemicals. Connections OK via CH pump. Coupled Feed and Exp pipes together in tank and closed this connection when flushing each individ. rad.

Any insights helpful - have tried searching but no dice.

Have looked for anti-gravity(?) device but

 

[Porker]

I have powerflushed my system twice. Once myself with hired kit and once a plumber did it. Neither time made a lot of difference. I've got the typical pyramid shape where it does not get very warm. What does work it seems but I've only done one rad is to take the rad off, take it outside and blow it through with a hosepipe. The only problem is that it can be messy and bleeding my system takes for ever. (27 rads!)

 

[ChrisR]

Chemical choice is important. Which have you tried? DS 40?

[ Took out a line here - brain was elsewhere when I wrote this - as chris H points out]

Using 2 people, inverting the rad in the garden with say 1/3rd to 1/2 full of water is pretty damn effective!

 

[alban]

Chemical choice is important. Which have you tried? DS 40?

Using 2 people, inverting the rad in the garden with say 1/3rd to 1/2 full of water is pretty damn effective!

FX2 - the Kamco-supplied desludger. Powerful, but I'm going for broke!

The 'garden' approach I tried with two rads - it took a lot of effort, was messy ++ and it's really the boiler I'm after to desludge - does P/fling really get a good flow through it with all the rads closed off?
Where do I attach the suggested ball valve exactly, Chris?

Thanks for all the replies.

 

[Slugbabydotcom]

When flushing from the pump position your boiler is in parallel with the rad you're trying to blast. An extra (full flow ball) valve is suitable to stop it.

Doesnt make sense to me Chris

By following instructions you create a circuit of which the boiler is constantly a part.

When you remove the pump and flush from there, the water is constantly drawn through the boiler, so that is bound to be the most cleaned part of the system. It makes a circuit with whatever else is available so if there is a by-pass it must be closed, anti gravity valves must be disconnected to allow flushing both ways.
The system feed and vent must be capped. Rad valve change plugging kits are inadequate as I found out the hard way
By isolating all the rads except for the one you are flushing a decent powerflusher [the one I use is a Kamco cf30] this will create a circuit with each individual rad and the boiler in series. If it doesnt and Chris's garden method doesnt work then the rad needs replacing.

Powerflushers remove sludge and are good at doing that, but nothing will work if they are internally rusted solid.

Kamco say that systems of over 25 rads should be isolated and worked as smaller zones.

I say that a powerflushing tool cant count and another 2 rads wouldnt make much difference anyway, especially if you are flushing from the pump which is the best way.



EDIT>

Just re-read your post and the following springs to mind.

Check TRV's aren't locked shut ... Sometimes they stick in the closed position. Also older one way TRV's can close shut if they are flushed the wrong way. Modern 2 way TRV's dont have this drawback.

When you joined the feed and vent pipes you may have created another circuit which reduces the flow to the rad you are working on. Capping them would produce better results

it seems to overheat and shut down on any setting above Min.

Your pump could be failing! Is it old? and is it up to the job?
I would expect to see a commercial sized pump on a large system like this.

Could be a boiler stat on its way out. Its normal operation is to turn the burner off when it reaches temperature and on again when its below a set level. It's not unusual for a bit of kettling to occur just before it turns off the gas.

 

[bathjobby]

Putting aside wether you are corgi registered or not and just discussing your scenario; Inside your boiler cabinet (positive pressure on this model so only corgi regs should remove case and break seal, enough said), usually the bottom left hand corner of the heat exchanger, there is a threaded drain plug sticking out. I guess that unless you can get all the impurities into solution when you power flush, the boiler will always act like a sump and after so many years will collect the impurities........... Make any sense !

 

[alban]

Bathjobby or anyone
You wrote that HE on Netaheat has drain plug lower left hand corner but couldn't see it when heating engineer came round. Just a bolt to secure the wall of combustion chamber on each side.
Diagram on Partsarena (Netaheat MkIIF) shows no plug but shows two plates bolted on to each side of the HE both with a seal. If these are removed can you gain access to the main chamber to de-gunge it without removing whole thing from boiler, do you know?

Tried chemicals, powerflushing, changed pump, checked mot valves all to try to stop boiler overheating and cutting off when turned above Min. setting. Fan OK too. Presume some clogging in HE and reduced flow causing problem??
Cheers

 

[bathjobby]

Can't help further I'm afraid. My experience is related to a Potterton Netaheat 80 which has the drain plug as described.