Corrosion in system

[rkanaga]

I've finally got to the bottom of my recurrent air/ gas problem…..

To recap..

http://www.ukplumbersforums.co.uk/central-heating-forum/55434-air-open-vented-system-new-post.html


We have an open vented fully pumped system with a 3 year old Vaillant Ecotec condensing boiler which replaced an ageing non condensing boiler in a 30 year old system.

About 7 months ago we had a slow leak from an underflow rad feed pipe buried in screen. This was dug up, cut out and a new section of pipe welded in. Unfortunately as this was a slow leak it had probably been going on for at least a month and so major drying out works were required before we could put the flooring down again etc, Very very traumatic to say the least! Thankfully although the pipes were buried in screed the leak was due to the pipe having been bent to go round a gas pipe (! yes I know!) and the rest of the pipe was fine. Furthemore the pipes were correctly wrapped in denzo tape and were in good condition so (fingers crossed!) I hope that we are not going to have problems with pipes corroding from the outside everywhere under the screed.

Anyhow since then we have had recurring problems with pumps becoming noisy and air in he system

BG have come a number of times and simply fit a new pump which is not a permanent solution.

Finally a more diligent BG guy came round and took the pump head off. This showed that the pump vanes were full of metallic crud. He cleaned the pump as a temporary measure. Clearly the problem is corrosion in the system.

BG are now proposing fitting a magnetic filter to filter any remaining debris.

The heat exchanger is almost certainly at least partially clogged as when we first got the pump working again the boiler was knocking loudly. It was better if you set the temp to a lower setting. This has improved now however and the system seems to be able to draw water through the boiler with a set temp of 62 degrees.

Gas is sell accumulating in the system both at the bleed valve by the hot water cylinder and in one particular rad upstairs. The rad upstairs only accumulates air when the central heating has been pumping, not when we have been using hot water only.

The system is not leaking now as I have tied up the header valve and the level does not drop.


My question/ concerns are as follows:

I am paranoid about not getting further leaks after the trauma to the family (with small kids) of 4 months of drying out and repairs last time.

Why is gas still being made? No new water is being drawn into the system and Sentinex was put in after the leak was repaired. Why is the system still corroding? Surely the fact that no fresh water is being drain in and Sentinex was put in after the system was refilled should prevent this? Is the presence of magnetite crud in the system (presumably at the bottom of radiators and/or in the heat exchanger) feeding this process?

Is draining the system down and fitting a magnetic filter the right thing to do? Should we have the system flushed with cleaner etc as well (given that the system will be drained to fit the filter?)

Should we pre-emptively change the heat exchanged in the Vaillant? (the part seems to be about £90, but I'm not sure about the labour. Again the system is going to be drained anyway so would it make sense to get this done at the same time?)

Above all what can we do to minimise the chance of further leaks? Will the corrosion affect the steel rads only (bad but not catastrophic) or are the aluminium rads (Farral type) and (heaven forbid) the copper pipes (some of which are as I said underfloor!) at risk as well?

Thank you so much for any help. I desperately want to make the best choice quickly to end this nightmare!

Robin.

 

[chris watkins]

First off Robin are BG still involved in anyway?
I only ask because you would expect one of the largest players in the industry to be able to solve your problems or at least go through all of the above issues & give you your options, surly that is what you pay an expert for ?
Strongly suggest you employ a good independent heating engineer who can check out a number of thing on-site with you, before providing advice & quotations to sort you out.

 

[grow_fins]

Did it not have a cleaning agent added when it was originally drained and refilled? Or after the BG chap cleared the muck from the pump? (Just answered my own question) Anyway, it should be cleaned, and then drained and refilled a few times to clean out the cleaner and the remaining crud. Adding a filter afterwards wont hurt either.
John

 

[rkanaga]

Thanks to both for replies.

Yes BG are still involved and I hope they will sort the problem out. I just want to be sure that the advice they are giving is correct and understand the issues in my own mind.


It sounds that having the system flushed through with cleaner would be sensible before fitting the filter.

What do you think about changing the heat exchanger? Should that be done now or wait and see given that it seems to be working at present and not restricting flow too obviously?

What I can't understand and what concerns me is why given that the system was drained and refilled and Sentinex was put in after the leak is gas still being produced? the main issue in my mind is to stop the corrosion continuing so as not to be faced with leaking radiators or worse down the line!

(If the corrosion continues is it likely to affect the copper pipes and aluminium rads or just the steel rads btw? Going away for a week at Xmas. I might isolate all the steel rads if it is only them at risk just to be safe!)


Thanks again


Robin.

 

[Killy Bing]

How old are your radiators?

 

[rkanaga]

How old are your radiators?

30 years. We have a mixture of standard Steel ones and 5 or 6 Farral aluminium ones

 

[chris watkins]

Thanks to both for replies.

Yes BG are still involved and I hope they will sort the problem out. I just want to be sure that the advice they are giving is correct and understand the issues in my own mind.


It sounds that having the system flushed through with cleaner would be sensible before fitting the filter.

What do you think about changing the heat exchanger? Should that be done now or wait and see given that it seems to be working at present and not restricting flow too obviously?

What I can't understand and what concerns me is why given that the system was drained and refilled and Sentinex was put in after the leak is gas still being produced? the main issue in my mind is to stop the corrosion continuing so as not to be faced with leaking radiators or worse down the line!

(If the corrosion continues is it likely to affect the copper pipes and aluminium rads or just the steel rads btw? Going away for a week at Xmas. I might isolate all the steel rads if it is only them at risk just to be safe!)


Thanks again


Robin.

So your so call expert is not an expert are they, if you are asking on here you clearly do not trust them & it would seem on present form you are correct ??
Just as a point on interest who installed the new boiler 3 years ago ??
No one on hear would dream of installing a new boiler on an old system without first cleaning the system & fitting a filter to protect the new boiler with its very small water ways. The manufacturers guarantee would be null and void if we did not clean first.
The gas you keep getting is most likely to be air drawn in via the open vent / cold feed of the open system. System needs to be investigated to find out what is happening.
Flushing / cleaning the system with the boiler in place & without a filter would just lead to more muck going into the boiler (which it sounds like has already got reduced flow rates)
I think you are getting a little paranoid when all you need is an experienced independent heating engineer, something it seems is not available in BG.

 

[rkanaga]

So your so call expert is not an expert are they, if you are asking on here you clearly do not trust them & it would seem on present form you are correct ??
Just as a point on interest who installed the new boiler 3 years ago ??
No one on hear would dream of installing a new boiler on an old system without first cleaning the system & fitting a filter to protect the new boiler with its very small water ways. The manufacturers guarantee would be null and void if we did not clean first.
The gas you keep getting is most likely to be air drawn in via the open vent / cold feed of the open system. System needs to be investigated to find out what is happening.
Flushing / cleaning the system with the boiler in place & without a filter would just lead to more muck going into the boiler (which it sounds like has already got reduced flow rates)
I think you are getting a little paranoid when all you need is an experienced independent heating engineer, something it seems is not available in BG.

Sure I understand that.

The system was put in by a local firm (mid sized not a small company) and they did flush through the system first. They did not however fit a filter.

I'm pretty sure that the F/E is not drawing in air however. The header is way above the boiler (2 floors.) i've also tied up a water bottle filled with water up to the open vent and the water is neither added to nor sucked up, so I really don't think that this is the source of the air. as I've also tried tying up the ball valve for 24 hours and the level in the header tank does not drop at all, I'm pretty sure that there is no further leak of fluid from the system.

What I don't know is whether corrosion and hence gas production can continue once the system is:-
1) no longer drawing in fresh aerated water
2) filled with corrosion inhibitor which is now not being diluted by fresh water?

(thinking out of the box the only other way I can think of for fresh water to be entering the system without any obvious drop in the header tank level would be for a leak within the hot water cylinder causing a mixing of the hot water and the boiler water. Is that likely?)

I may sound a bit paranoid, but you would be too after having gone through the trauma's that we have!


thanks again

Robin

 

[chris watkins]

Is there a difference in the water level between the F&E & the main cold water storage cistern ? if so then its not the coil cos one of the two cisterns would be overflowing.
Corrosion can occur between dissimilar metals (electrolytic) depending on there position in the electromotive scale i.e. +/- volts. The water in the system acts as the electrolyte, oxygen is not required. A corrosion inhibitor is required that is suitable / designed for systems containing Aluminium. Not sure Sentinex is OK can you confirm?

 

[Killy Bing]

sentinex ?never heard of that but I think you mean sentinel x100 ?? which is suitable for aluminium however what condition are the radiators in ? it's possible that a pinhole could be present allowing air to be drawn out but not allowing water to escape (yet).

 

[rkanaga]

Is there a difference in the water level between the F&E & the main cold water storage cistern ? if so then its not the coil cos one of the two cisterns would be overflowing.
Corrosion can occur between dissimilar metals (electrolytic) depending on there position in the electromotive scale i.e. +/- volts. The water in the system acts as the electrolyte, oxygen is not required. A corrosion inhibitor is required that is suitable / designed for systems containing Aluminium. Not sure Sentinex is OK can you confirm?

The level in the (2) cold water reservoir tanks in the loft is much higher than that in the F&E tank so I guess that rules out a leak in the hot water cylinder coil - thanks

 

[rkanaga]

sentinex ?never heard of that but I think you mean sentinel x100 ?? which is suitable for aluminium however what condition are the radiators in ? it's possible that a pinhole could be present allowing air to be drawn out but not allowing water to escape (yet).

Yes sentinel x100 sorry.

The radiators 'look' in ok condition. I cannot see any leaks but then you can't see every aspect of them. I'm sure that the header tank level is not going down but how do you trace a pin hole allowing air in but not water out yet?

I'll test the gas with an upturned jar and a match later to see if I can clarify whether it is air or corrosion produced gas

Robin

 

[Killy Bing]

A long shot but you could isolate all the steel rads and see if you still get the air after a few days?

 

[rkanaga]

I could do that, good idea. If I just run the hot water circuit and not the central heating (the system is fully pumped with 2 honeywell motorised valves after the pump to feed the central heating and hot water circuits separately), I still get a lot of air collecting in the automatic bleed valve next to the hot water cylinder. Does that provide any additional information about the source?

Presumably if only the hot water circuit is one then the air/gas must be coming from somewhere other than the radiators? IN other words the source must be at least in part within the boiler, primary feed and expansion circuit and hot water circuits?

 

[Killy Bing]

you're in effect between a rock and a hard place with this. as the source in reality could be from anywhere, a pin hole leak, a radiator breaking down internally, a soldered joint or even a compression joint. you could go and change all of the radiators and hope that solves it. you could even re plumb the whole system !!! it could even be your pipework is currently installed in such a way it retains pockets of air !! I personally would look at installing a few spirovents to vent the air as it forms. it won't solve the route of the cause but you could end up chasing your tail for years trying to find out what's doing it. sadly without us having a look in person we are limited. you have been great with your ideas, descriptions and listening to our advice!!

 

[rkanaga]

you're in effect between a rock and a hard place with this. as the source in reality could be from anywhere, a pin hole leak, a radiator breaking down internally, a soldered joint or even a compression joint. you could go and change all of the radiators and hope that solves it. you could even re plumb the whole system !!! it could even be your pipework is currently installed in such a way it retains pockets of air !! I personally would look at installing a few spirovents to vent the air as it forms. it won't solve the route of the cause but you could end up chasing your tail for years trying to find out what's doing it. sadly without us having a look in person we are limited. you have been great with your ideas, descriptions and listening to our advice!!

thanks

my other thought is that since this problem only started after we has a leak and the (old system with the new boiler) system had been fine prior to this I don't think it's a design issue.

bur as you say many other potential causes!

thanjs again, I'll keep working on it!

 

[rkanaga]

One more thing just so I can sleep at night, am I correct in thinking that if any leaks occur as a result of this they are likely to be from the radiators and not the underfloor copper pipes (which are wrapped in Denzil tape)?

another underfloor leak would be the final straw!