Central Heating flushing update and a couple more questions

[John Kelly]

The story so far. British Gas recommended I pay them an exhorbitant=20 amount to clean out (powerflush) the system. Discovered that the=20 chemicals used cost < =A340 and it's doable on your own albeit without the= =20 powerflush bit.

I drained the entire system twice which took a few hours and the water=20 went from blackish to clear then to brownish. Couldn't figure out why it=20 was coming out brown so checked the header tank in the loft. Disgusting.=20 Ended up in the loft with various buckets and sponges/cloths cleaning=20 out the header tank. 1 hour later flushing the system again - another=20 couple of hours. Went from brownish to clear after two flushes.=20 Excellent. Put the sludge removal compound in (this was 4pm) and=20 refilled the system. The radiators upstairs were incredibly hot - result=20

- but downstairs were incredibly cold - not so good - so turned off all=20 the upstairs radiators to force the pump to do downstairs. This still=20 didn't make them all work. I think what happens is the sludge removal=20 stuff is so good that it absorbs all the crap in the system and then the=20 pump has to pump it all round until you remove it a week later so=20 leading to some blockages (I'm making it up here so could be wildly=20 wrong). All the sludge had collected downstairs as I found out when I=20 bled a litre or two out of the radiators to get them going. This worked=20 but the water coming out was disgusting and previously had been clear.=20 This was about 6pm when it was finally all up and warming the house=20 again but the house had been open all day and no heat (or hot water)=20 available. Cold kids and wife :-(

Anyway next weekend I'm draining it again and then adding the inhibitor.

Couple of questions

I put the sludge removal stuff in the tank in the loft. Presumably=20 there'll be some left in the tank. Is it best to clean this out (again)=20 before putting the inhibitor in?

I'm going to put thermostatic valves on the upstairs radiators once the=20 system is empty. Firstly are there any recommended types? Secondly I'm=20 not sure on one of the radiators which pipe is the one where the on-off=20 bit goes as it didn't have any caps on when we moved in. Does it matter=20 which side the valve goes?

Thanks

--=20 John Kelly

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[Christian McArdle]

Not if you buy bi-directional valves, the lockshield and TRV can go either end. Although it is traditional to put the TRV on the flow side, they actually work better on the return side, as the rad temperature is lower here and they sense room temperature more reliably.

Christian.

[John Kelly]

Right - I'll have a lookout for them. So I could be better off putting

*all* my valves on the return side then? That's one of the problems with this stuff. When I was young it was simple and I understood it all and just did it. Now it's all gone technological and needs to be thought about before doing it :-(

[mcbrien410]

John, the process I've adopted over the years is to turn ALL radiators OFF except one. Then turn the C/H pump on to the high speed setting. Then start to drain the system, ensuring that the ball c*ck in the header tank is allowing it to continuously fill up. I ususally flush each radiator for about ten minutes. Now turn ON the next radiator and turn OFF the first radiator. Work your way from upstairs to downstairs as **it flows downhill. I do have a slight problem clearing the "dump" or "leak" radiator as this is not on the pumped circuit. I have to drain this by hand. A few years ago I hadn't drained this "gravity" fed radiator for years and in one corner there was a "cold curve" where the sludge had settled. Even with about 3 meters of hydrostatic head of water on it the sludge would not shift. I shifted that with a Chop Stick.

Recently I looked into a mates header tank and I asked him why there was a steel plate on top the water. He looked puzzled. It wasn't a steel plate, it was a rusty slime almost hard. I advised him to dig that out BEFORE you ever drain the system.

I try and do this once per year but it does slide to two years now and again.

Chris.

[John Kelly]

Hmm, my understanding is obviously lacking. Which one is the dump radiator (how could I tell?).

Ta.

Scary. I actually thought that mine was coloured brown before I cleaned it out :-)

[mcbrien410]

John, the dump or leak radiator, if you have one, is generally across the indirect heating loop of the hot water cylinder. Mine is a solid fuel system with NO automatic valves and timers. The dump/leak radiator is there to absorb excess heat if there is a pump failure. It is NOT pumped and is just in a gravity fed loop of its own.

Chris.

[Set Square]

You can tell which is flow and return when the radiator is running, by feeling the pipes - the flow pipe is hotter than the return pipe.

Probably. Note that some bi-directional valves *do* care which direction the flow is in - and have a little 2-position gizmo which has to be set according to which way round you're using them.

[John Rumm]

One problem I found with a pegler terrier II bi-di valve was that one the return side it would whistle as it began to close down and partly occlude the flow. In the end I had to swap it to the flow side to get rid of the noise...