Viessmann 222 leaking PRV

massapprentice

Has anyone had experience with a Vitodens 222 leaking water out of the boiler PRV.  We replaced the PRV and still leaks. Note on side of combustion enclosure reads: “In case of water discharge from PRV, check DHW heat exchanger”. Could a fouled DHW heat exchanger cause this issue?  I put a pressure meter on the hydronic system and at some point the pressure overnight reached 40psi, obviously triggering the PRV. The unit is only 2.5 years old after being replaced under warranty b/c of previous main heat exchanger leak and failure. 

Jamie Hall

This is hot water heat? What size, and what is the condition of, the expansion tank?

Yes, a leaking heat exchanger will cause the pressure to rise -- and stay up. But an expansion tank problem will cause it to rise and fall.

massapprentice

Hot water yes. Its 125,00 btu. Combi boiler. Expansion tank is ok. Pressure was at 15 when checked. System typically running at 12. Problem only seems to occur when the hot water is run for extended periods. 

Jamie Hall

To be clear: this is the pressure relief valve, rated at 30 psi, on the hot water heating side of the boiler, not the pressure relief valve, rated at probably 150 psi, on the domestic hot water side?

Derheatmeister

massapprentice said:

Hot water yes. Its 125,00 btu. Combi boiler. Expansion tank is ok. Pressure was at 15 when checked. System typically running at 12. Problem only seems to occur when the hot water is run for extended periods. 

1.Did you relief the pressure on the Hydronic side of the expansion tank prior to checking the Air/Nitrogene pressure on the expansion tank ? (This is also the propper way of adjusting it)
2. IMO if your diaphragm on the expansion tank should be 2 psi less than your cold fill pressure
3. Is your expansion tank sized correctly ?
4. How old is the Expansion Tank and in which position is it mounted ?

Pictures of the install may help.

massapprentice

To confirm, this is the 30 lb PRV coming off the boiler itself, not the PRV on the DHW tank. 

The boiler was isolated and drained when checked.  

The expansion tank is packaged in the boiler from the factory so its size and position I have to assume is correct. 

psb75

To be clear, the 222F boiler has both an inboard expansion tank as well as a DHW tank.

Jamie Hall

massapprentice said:

To confirm, this is the 30 lb PRV coming off the boiler itself, not the PRV on the DHW tank. 

The boiler was isolated and drained when checked.  

The expansion tank is packaged in the boiler from the factory so its size and position I have to assume is correct. 

A very dangerous assumption...

Derheatmeister

massapprentice said:

To confirm, this is the 30 lb PRV coming off the boiler itself, not the PRV on the DHW tank. 

The boiler was isolated and drained when checked.  

The expansion tank is packaged in the boiler from the factory so its size and position I have to assume is correct. 

1. The domestic reliefvalve should be a TP valve (Temperature and Pressure) ...Hopefully not a PRV !
2. If you isolated the boiler, drained it and checked the pressure on the intergrated expansion tank ...What was the pressure on the Air side of the Exp. tank?
3. Assuming that the intergated expansion tank is sized for all size systems is as Jamie said a "A very dangerous assumption". These intergrated flat thermal expansion tanks are sized for a small European style installs and we always install anouther external one !

If you don't want to calculate the thermal expansion rate i understand that since this can some time and make you head hunt..
I have walked onto service calls like this where the reliefvalve was leaking for years due to Assumptions of the original installers..
I have done temporary Midnight service call hookups with Braded Washmachine hoses and proper sized/adjusted expansion tanks just to proof the lack of proper expansion tank sizing prior to hardpiping it..
Maybe you could do a experiment with an additional external expansion tank..
Hopefully you can figure it out..