Low pressure on shared solar/gas DHW


Old 06-04-13, 10:22 AM
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Low pressure on shared solar/gas DHW

Hello, thanks for doing this. I have just signed on.

I manage a combined space heating and domestic hot water system which serves four households plus the common space in our cohousing community. 160 vacuum tubes on the roof heat two 120 USG storage tanks containing potable water, and those feed into a gas boiler. The boiler is a Triangle Tube Delta. I am unable to verify the model number (doesn't seem to be written on the unit and I have temporarily misplaced the manual).

The system is 9 years old although we have made some modifications in the meantime. Two years ago I had a plumber replace the temperature control valve at the boiler, because water temperatures were fluctuating. He did not replace it with the original model.

This past week we had low temperature and low pressure on the hot water. I checked and the tempering valve was putting out only cold water, although hot water was coming to the valve. I got the same model as the one that was installed 2 years ago, and installed it. It is a Watts Series 1170C-M2. Since then, the water is hot enough but the pressure is very low at times. It seems to be fine for some hours, then low. The cold water pressure is fine. I did check, when installing the new valve for obstructions in the pipes coming in (flowed some water out to make sure it wasn't crapped up).

I have checked the pressure on city water coming into the system and it's at 40 psi.

Any suggestions as to how this problem might be caused and how to rectify it?
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Old 06-04-13, 11:45 AM
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P.S. I took out the new tempering valve and ran a little water through the 3 lines connected to it, to check for obstructions. I did not find any. So far I believe it's behaving the same. Pressure OK at first, then drops.
Old 06-04-13, 11:46 AM
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We probably would need a diagram to see how things are piped. Pics may help but its probably a hodge podge of stuff and pics will not tell the whole picture.

40 psi is low incoming water IMO. Possibly you have a PRV valve gone bad?? That should be near where the main comes into the home.

Posibly an old gate valve broke and is not fully open?

Just some thoughts....
Old 06-04-13, 04:43 PM
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Your delta will be a PG 25,35, or 45.
100,000 to 199,000 BTU input.
There were some modulating deltas sold just prior to the end of the model.

I seem to get the balance of the delta service in Ontario, which is a double edged sword...

If you can get some pics of the system piping we might be able to help better.
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