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Author Topic: Stagnation problem  (Read 333 times)
9fingers
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« on: September 23, 2018, 11:39:59 AM »

I've had a solar thermal system running perfectly for several years now but recently noticed that the top on the roof sensor has been showing embarrassingly high temps of 150C and above and increased pump noise.
I presume that the system is stagnating. System pressure has remain at 1 bar ish when both hot and cold since my self-installation so no leaks.
In the recent cooler, sunless weather I got round to bleeding the collector and got what seemed a lot of air(gas?) out to the extent that the pressure has dropped to just below 0.5 bar. Pump seems quieter and I have yet to look at the temperatures when the sun next comes out.

Where has all this gas come from? Does this mean my glycol solution (40%) has become acidic and the gas has come from acid attack on the pipes?
I've ordered some universal pH indicator strips from ebay and will do some tests. The glycol solution is still near clear with no significant colour change from original.

If it turns out it is acidic can I just add some mild alkali to restore the pH?

TIA
Bob
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desperate
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Backache stuff!!


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« Reply #1 on: September 23, 2018, 05:37:43 PM »

It might be the EV that has started leaking across the membrane, it wouldn't show up as a pressure drop at the guage but would allow gas into the loop, try briefly venting the schrader valve on the EV to see if any fluid comes out, if it does you need a new EV.

Desp
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www.jandhbuilders.co.uk

still a crazy old duffer!
9fingers
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« Reply #2 on: September 23, 2018, 05:50:10 PM »

It might be the EV that has started leaking across the membrane, it wouldn't show up as a pressure drop at the guage but would allow gas into the loop, try briefly venting the schrader valve on the EV to see if any fluid comes out, if it does you need a new EV.

Desp

Hmm! an interesting thought! Thanks Desp, I'll check that out.

Bob
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