ARRRRRRGH! Corrosion!

[iep]

6 months ago we renewed all the radiators in our house and 90% of the pipework (replaced microbore with new 15mm). In total we have 6 large double radiators and 4 medium singles. The boiler and pump were not changed.

When the system was first tested, it was filled with water and run for 1 day to check for leaks. Once no leaks were found, it was drained down and filled again this time with x100 inhibitor added prior to filling (one bottle).

All has been good since then but when I checked in the F&E tank today I found that the water was dark brown and a layer of orange 'scum' had collected on the surface. It looks like the system is corroding quite badly despite the x100.

I don't believe there are any leaks in the system (that might cause dilution of the x100) as the system was run for one week after it was commissioned with the mains feed to the F&E cistern switched off and the level in the tank did not drop.

I have also seen no evidence of 'pumping over' that might cause air to dissolve in the water. I started and stopped the system while watching the vent pipe in the F&E tank and no water flowed out of the pipe.

I have turned off the mains water to the F&E cistern again to check if a leak has developed over the last 6 months and plan to clean the system out with x400 for the next few days before draining down and refilling this weekend with two bottles of x100 added.

Is there anything people can think of that might cause this corrosion and anything else I should try to fix it?

Cheers,

iep

 

[Slugbabydotcom]

You seem to have the fixing it side of things well weighed up.

I've got 4 thoughts as to the possible cause of the problem.

1. Loss of water/inhibitor from the system or not enough inhibitor in the first place.

2. Vents can suck in air as well as pump over. This can be caused by a bad system layout ie. vent and feed location with regard to the positioning of the pump. I would expect you to be regularly getting some air in a radiator if this was the case and possibly for the next idea

3. It has been known for old pumps especially grundfoss to suck in air through the seal behind the big screw on the front. Quite rare but I've seen it a few times. This happens when the pump is old so the answer is a replacement.

4. Maybe this is residual contamination from before the last treatment.

 

[iep]

Thanks slugbabydotcom.

I ran the heating through the night with the F&E tank cistern switched off and it does not appear to have lost any water so far. So, I'll keep an eye on it but I don't think we have any leaks.

I guess it could be gulping air in through the vent in the F&E tank but the feed and vent are tee'd right next to eachother and the layout looks to be fairly textbook. Also, there is only a minimal amount of air collecting in the highest rad (needs to be bled for 5 seconds or so once per month) so I suspect that might be hydrogen from the corrosopn rather than air (I should have done a flame test to prove this yesterday but forgot).

So, the only two things I can think of are that:

1. I need to add more than one bottle of x100 to the system (I only put one bottle in when I filled the system)

2. The new radiators were not properly cleaned out after manufacture. I asked the merchant when I bought them if they would need to be flushed before installation and he told me they did not. Maybe he was wrong?

Cheers,

iep

 

[iep]

With a problem like this, is there any merit in taking the rads off and cleaning them out with a hosepipe or can I expect the x400 to do a good enough job on its own?

There are no cold spots or flow issues yet so I don't think there is any major build up od sludge. However, I would like to nip this in the bud before it becomes a real problem.

Cheers,

iep

 

[Jake1886]

I'd run it for a while with X400 and then give it all a good mains flush through. Then give the F&E a good scrub out.

Should remove most of the carp out the system.

 

[iep]

How do I go about giving the system a mains flush through?

I guess I could attach the mains water supply to the F&E tank's cold feed and block up the vent? This sounds like a much easier plan than removing all the rads. If you could give me a description of how to to it, that would be hugely appreciated.

Cheers,

iep

 

[Jake1886]

Yep block the vent and hook up the main to the cold feed. Run a drain/dump hose from a drain cock to a drain.

Isolate the boiler if you can.

Open all radiators and let the mains work a fair bit of the carp from the system.

Then close all the rads except one and let the mains flush through that single radiator until water flows clear. Then close that radiator and move to the next, repeating the sequence till all rads are flushed.

You need to be careful though, as if any of your rads are weak etc they may split! And the glands on your rad valves may well leak etc.

If you don't feel confident then get a professional round

 

[iep]

Thanks Jake1886. All the rads and valves are brand new (well, 6 months old) so I'm going to hope that they will be okay.

I'll have a shot over the weekend and report back on how it goes.

Below is a diagram of our system that I drew up last night. By the look of it, I can isolate the boiler by closing off the valve on the pump which will stop water flowing through the boiler. If I then open the radiator return side drain cock, I can force water through all the rads one by one.

View media item 28257
Thanks again,

iep

 

[Jake1886]

Oh if the rads are new then there shouldn't be any problems, may still get a few gland nuts leak though.