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

[solarman216]

This is a complicated issue, and most plumbers/heating engineers do not understand it, the cold feed and vent should be as close together as possible, the old idea was more safety orientated, in that the vent should be on the flow from the boiler and the feed should be after it by no more than 6 inches and preferably looped to feed from under the flow pipe, but this can cause issues, typically the feed can get restricted, more modern ideas favor, the 22mm vent being the only connection to the flow pipe with the feed tee'd into the side of it close to the flow pipe, pump over or suck back are both bad for your system and in such cases you need to keep a close eye on your inhibitor concentration, regular draw offs and test with wire wool are good, inhibitor can be degraded in less than a year in both situations, Rick

[rustic]

Thanks for the advice Rick, I'll see what I have. Be a while before I can get to it now, At daughters for two days, then oncologist appointment on Friday, then drive across to Crewe for my Aunties funeral. We only saw her last month and she had reached 100 years old.
So keeping us busy.

One odd thing...
The new three port valve last night was hotter than the pipes, even though the heating was off.
The valve was being powered to keep the divert to heating even though the heating was off and the boiler off etc...

A quick tour of the internet...
Apparantly the valve stays in the position as to what ever was used last... so if Hot water... it is unpowered and stays diverted to hot water.
If the central heating was last used, the motor runs ie stalls to keep the valve open to the central heating.
Apparently this is fairly common, and in the last 20 years I never noticed...
The solution is to run the hot water for a few minutes after the central heating... and it switches off the power
I know the valve is designed to work like this, and only uses 6 watts of energy, so that's why it gets warm.
I don't like it though.. maybe why the valve has only lasted 20 years lol...
I will be reprogramming the timer to suit.
Rustic

[solarman216]

yes it is a quirk with three port valves, one of the reasons I do not like them, Rick