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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 22024
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have a Buderus gb142 and am having a similar problem to DA

Customer Question

I have a Buderus gb142 and am having a similar problem to DA who you helped. I am not getting any hot water; the LED flame indicator light is not coming on and I am getting a repeating H7 P9 code, which I understand means low water pressure. After reading your string with DA I ran through the steps you gave him, but could not resolve the problem. The water pump is working, at least I can feel it slightly vibrate. Any ideas?
Submitted: 2 years ago.
Category: HVAC
Expert:  Rick replied 2 years ago.
The display indicates the water pressure is too low. I don't know what thread you're referring to. The first thing you need to do is to try to bump up the pressure although for the most common system config the pressure should be maintained automatically. What specifically have you tried so far?
Customer: replied 2 years ago.
OK. I tried reset, turned the boiler on and off, checked for loose wires at both the boiler and the water pump, checked the water pump to see if it was running (felt vibration). When I did the reset the first time the boiler came on for approximately 3 minutes, could see the flame, but the Burner Operation LED did not light. After the boiler shut down the red light on the top corner of the Universal Burner Automat started blinking. When I turned the system off and then back on that light has not come back.
Expert:  Rick replied 2 years ago.
Ok so you didn't do anything to address the low water pressure issue. You need to locate the small diameter (typically 1/2" nominal) water line that feeds the boiler. There should be a device (a feed valve see attached pic for typical) on that line that regulates the water pressure let into the boiler/system. This device is likely malfunctioning. There is a way to bypass it that might work to bump up the pressure. I need to know just what brand and model feeder you have so I can tell you how to put it on bypass/fast fill. Also be sure any shut offs on that branch line are open. One "exception" to all this is if the system is closed and filled with anti-freeze. If that's the case you'll probably have to call a plumber to add anti-freeze.
Customer: replied 2 years ago.
I thought that this code referred to DHW?
Expert:  Rick replied 2 years ago.
The number following the P is the system pressure. Anything below 14 and the system won't function.
Customer: replied 2 years ago.
So the P designation refers to water in the boiler, not the DHW pressure? This is contrary to the prior post and thus my confusion. This is a closed system as far as I am aware, it is a radiant heating system. I have not tried to turn on the heat. the problem is with no hot water. I will try to get the brand and model # ***** the feeder now.
Expert:  Rick replied 2 years ago.
DHW pressure is irrelevant to boiler operation. If the system pressure isn't at the minimum the boiler won't function. If the boiler doesn't function you won't have DHW assuming you have an indirect fired water heater.
Expert:  Rick replied 2 years ago.
I have to leave for about an hour (or less). I'll respond when I return
Customer: replied 2 years ago.
The feeder is a Taco Model 329-3; Size 1/2"; Set 12 psi; Range 10 - 25; lever is set to far right position.
Expert:  Rick replied 2 years ago.
Perhaps it's your orientation but this feeder bypass lever would normally be moved to the right to put it on fast fill. Try moving it to the opposite side and see if you hear any water flowing. If you do then watch the (analogue) gauge and move the lever back when it get just above 15 psi. If nothing happens when you move the lever then check to be sure the (manual) shut off valves are open. I'm assuming you have no anti-freeze in the system. If you don't this is not a closed system. If the pressure doesn't stop rising when you move the lever back then close the manual shut off.Back in an hour
Customer: replied 2 years ago.
I don't know what you mean by a closed system.
Expert:  Rick replied 2 years ago.
It doesn't matter. Just try what I outlined above if you want to take a shot at fixing this. You caught me with 1 foot out the door. I really do have to leave now. I'll respond when I get back.
Customer: replied 2 years ago.
I moved the lever to the right and water started flowing. I let it run but the analogue gauge didn't budge before the pressure relief valve blew and I could not get it closed, so much of the water drained out of the system before I figured out how to stop the flow.
Expert:  Rick replied 2 years ago.
Sounds like your gauge is busted. You need a working gauge to monitor the pressure before you try again. You're easiest option is to get a test gauge link the one in the link (try to get one with a lower scale than pictured 100 psi not 200 is best) screw it onto a boiler drain (hose type faucet) on the system and open the faucet/drain. Then try bumping up the pressure again while you watch this gauge. The feeder should have kept the pressure up automatically so it will probably need to be replaced but this should get you by until you can get that done.