How often to change Central Heating inhibitors.

[rustic]

Well the central heating went Kaput on Sunday, conventional pumped system, old fashioned cast iron boiler, and header tank. The boiler fired up and was able to heat the hot water, but not the central heating on its own, so the three port valve was suspected, but the fault wasn't like it was when it failed 10 years ago when it was a cheap and chearful motor exchange, the lever on the side felt odd, didn't return...
It could be the gearbox, or the valve body, rather than mess about I was 100% certain the valve was faulty, and a valve 20 years old must fail sometime, so part drain down time. Wow the header tank was full of gunge, so I connected a hose and syphoned off the gunge, and flushed the tank, before draining down.
So I tied up the ball cock, emptied the header tank.
The valve is upstairs, so I thought I would take another 2 gallons out of the heating system, from a drain downstairs. I took a sample and put some steel wool in there to check how good the inhibitors were... Now wait and see for a week or so lol...
I changed the valve, no water spillage, not a drop, filled up, all ok valve works, we are warm again...

Now... thanks for staying with me on this one....
How long do you leave chemicals in the system, before flushing out and refilling?
The internet has different ideas.
They say test the chemicals.... How ? Well this is where the steel wool idea came from...
I fully flushed it 7 years ago added inhibitors etc... I think it needs flushing again, but then web sites say... adding fresh oxygen rich water encourages corrosion......

Any ideas... it is not a cheap and nasty combi boiler with a thin aluminium heat exchanger with an 8 year life lol...
It is a cast iron Potterton boiler, with copper pipes, steel rads, copper immersion tank and header tank.
Many thanks.
Rustic

[davenclaire]

To be honest you shoulda proberly have flushed the rads out as well as the sludge usually collects at the lowest point and even your pipes cab furr up just as they enter the main pump.

If the inhibitors are doing their job then great but if the system still has crap in it they won't help much, a power flush mite

[briggie]

solarman ( rick ) is your man for advice on this one mate

[solarman216]

Hi Rustic, first can you tell me what colour the header tank water was, Rick

[rustic]

Originally Posted by solarman216

Hi Rustic, first can you tell me what colour the header tank water was, Rick

The water in the header tank was clear, but there were orange greasy deposites around the waterline and dark coloured bits in the bottom resembling bits of algae, breaks up into strands.

I assume the orange bits were ferrous oxide when in contact with the air.

I'm off to bed now as we are up early 4:30 am to go to see our daughter in the morning... beat the traffic lol.
Rustic.

[solarman216]

OK you need to be checking what happens when the hot water is on only, then CH only and last with them both working, what you are looking for is dribbles from the vent pipe or a slight rise in water level when the pump starts, and any change in temperature of the cistern water, but you haver a pipe feed/vent connection problem that needs addressing, corrosion inhibitors are only part of the protection, my guess is you will have dribbles from the vent, Rick

[rustic]

Originally Posted by solarman216

OK you need to be checking what happens when the hot water is on only, then CH only and last with them both working, what you are looking for is dribbles from the vent pipe or a slight rise in water level when the pump starts, and any change in temperature of the cistern water, but you haver a pipe feed/vent connection problem that needs addressing, corrosion inhibitors are only part of the protection, my guess is you will have dribbles from the vent, Rick

Clearly it's been like this since new, 20 years.
I'll have a look when we get back to see of there is any circulation.
Also to check where the over flow is in relation ship to the pump.

What would a solution be?...
The overflow pipe is only about 6" -8 " above the header tank, so only a minor increase in pressure could force water through the overflow.

At the moment, we are on middle pump speed, but most of the radiators are off, or the valves just cracked open for circulation.
Rustic