RESOLVED - Viega ProRadiant loses pressure and shuts off - Needed a new pressure/temp sensor

clutzer

Ecosystem:

• Boiler: Viessmann Vitocrossal 300 CU3A 199; runs a 25psi heating loop
  
• Mixing Block: Viega Hydronic Mixing block model 2883.7 (part 56160); hooked into the 25psi heating loop
  

Symptom: The mixing block usually reads "-----" for PSI which means the sensor is bad or the wire is broken or shorted. However, if does read pressure if you can "get the system going" (see image). That said, once I do get it going, the PSI slowly drops to zero and the system shuts down.

Troubleshooting: I took two loops out of the equation and trying to see if the pressure stabilizes. Basically I'm trying to find a leak. The two loops that I closed the valves for are in concrete slabs. The two loops that are still running are throughout the house, on the underside of floors. There is nothing leaking (at least visibly showing).

Question 1: Any thoughts on how to troubleshoot further? Could the Grundfos be bad? "-----" says the sensor is bad, but I wonder if it also means "too low to read"?

Question 2: Anybody know of any good Viega contractors in the Boston south shore area?

Jamie Hall

Electronic gadgets. Yoi don't happen to have a real mechanical pressure gauge hooked up do you?

hot_rod

Has it always done this? If pressure drops, could be pumping at the expansion tank PONPC. If it just started and drops to zero, it sounds electronically related.

To the left of the display is a Grundfos "vortex shedding" type sensor. They read two things either pressure and flow or flow and temperature depending on the version. Pull the stainless horseshoe clip to pull it out and replace.

Has a wire been clipped from the molex plug on top?

GGross

The viega literature is pretty clear --- means bad sensor or short in the sensor wiring. I would most definitely install a mechanical pressure gauge near the unit, I love my electronics but there is nothing like being able to reference an analog gauge in a boiler system.

If you had a leak you would need to be adding water to the system, are you adding water in between shutting down on pressure?

clutzer

Jamie Hall said:

Electronic gadgets. Yoi don't happen to have a real mechanical pressure gauge hooked up do you?

On the heating circuit from the boiler, yes. It reads 25psi which is what the Caleffi pressure reducer is set to. It's confusing to me that the psi doesn't eventually equalize while the valve is open... Instead, valve closes and pressure drops to 0.

clutzer

GGross said:

The viega literature is pretty clear --- means bad sensor or short in the sensor wiring. I would most definitely install a mechanical pressure gauge near the unit, I love my electronics but there is nothing like being able to reference an analog gauge in a boiler system.

If you had a leak you would need to be adding water to the system, are you adding water in between shutting down on pressure?

There's a Caleffi pressure reducer which I believe will keep adding water into the heating circuit. I just had an ah ha moment: if I close the valve feeding the Caleffi and heating circuit, I can monitor the analog pressure regulator and see if it moves.

clutzer

hot_rod said:

Has it always done this? If pressure drops, could be pumping at the expansion tank PONPC. If it just started and drops to zero, it sounds electronically related.

To the left of the display is a Grundfos "vortex shedding" type sensor. They read two things either pressure and flow or flow and temperature depending on the version. Pull the stainless horseshoe clip to pull it out and replace.

Has a wire been clipped from the molex plug on top?

I would say it ran well for one to two seasons and then degraded and became really fussy/inoperable. It was deployed in 2018.

That clipped wire is from a 4 wire that I was using to attempt to hook the mixing valve up to the boiler to call for heat (long painful story, but in a nutshell my radiant was value-engineered and a lot of shortcuts taken and the mixing valve just sits on the heating circuit and crosses its fingers that the boiler is producing hot water when it decides it needs to warm the radiant circuits.)

clutzer

As I type this, valve is in roughly the same position but pressure is well on its way to 0... (facepalm).

clutzer

RESOLVED: I ordered an entire new mixing block from supplyhouse dot com who had it in my hands the next day (free shipping!), no affiliation but I just wanted to call them out for having great order processing and shipping.

I swapped the computer (as the board PCB is updated) and the temperature/pressure sensor and that did the trick.



Thank you to everyone who responded to this post. I appreciate the support -- great community here.