GB 142 Hot water issues

Landry Mechanical

Dan always said don't do work for your friends or family.... Well, a little over a year ago I put in a GB 142/ 24 in my brothers house. The system consists of hydro-air, and a 45 gallon superstore indirect. He has a shower head which puts out exactly 3.3 GPM. As he explains it, most of the time he will run out of water after 10 minutes of shower time. Other times though it lasts for longer. He is not using any other fixtures when he is showering. I know this boiler is small, but it's the same set up as in my own house, only I am on natural gas, and I don't have the same problems as him. I am wondering if maybe the BTU content of the LP is effecting the situation. Is there a way to clock LP as you can with natural? Does the net BTU rating of 84,000 BTU's on the boilers nameplate  on natural become lower when it's on bottle gas?



Specifics of the install



Grundfoss 2699 pump, 25' of combined supply and return piping, about 12 1" elbows.



He says that once he runs out, he will go down and check the boiler, and it only will be about 120 to 130 degrees, and on full fire.





Thanks for your input guys!

Ray Landry

meplumber

Should go to high fire on DHW

If you are setup correctly, the boiler should go to high fire on a call for DHW. Something isn't right. May be coding or wiring. Or it could be a faulty tank sensor.



Are you using the buderus DHW sensor in the tank well? Or is this a zone off the heating system?

Landry Mechanical

re

The boiler does go to high fire but does not keep up. I have already changed the dhw sensor and verified resistance. This is piped in prior to the primary pump, so its not on the secondary side and it has priority.

Landry Mechanical

re

The boiler does go to high fire but does not keep up. I have already changed the dhw sensor and verified resistance. This is piped in prior to the primary pump, so its not on the secondary side and it has priority.

Mark Eatherton

Check valves?

Piped this way requires a check valve on both the DHW pump and the primary boiler pump. Although the DHW function is "prioritized", if a zone is calling for heat at the same time, and the check valve has failed, a significant amount of your flow is bypassing the DHW tank. If the boiler is running, the energy its producing is going somewhere, or it would be bouncing off of the high limits.



Try having him turn down all thermostats before he jumps into the shower and see if it makes a difference.



ME

Landry Mechanical

checks

Hi Mark



The check in the primary loop pump is OK. I know for a fact he loses heat on a dhw call because his hydro air unit blows cold air... another conundrum with the ecm blower I can't put in an inline aquastat. Does any have a chart for lower btu boilers coupled with indirects and how much the output should be?1

Mark Eatherton

Got it...

One thing that wasn't mentioned is water quality. If it is real hard, the heat exchanger could be limed up, significantly slowing heat transfer. This usually presents itself over time. It starts out fine but get worse as time goes on.



Also, a 42 gallon tank only puts out roughly 80% of its stored volume, or around 32 gallons. That would be your 10 minute shower.



Additionally, the aqua stat is high in the tank vertical profile, hence you could have a half cold tank before the stat even calls for heat, so you are playing catch up to begin with.



This is one of the main reasons I gave up using HTPs storage tanks. In order for them to work well, the heat exchanger needs to be fully immersed in cold water, hence the high positioning of the stat well. I prefer to use a reverse indirect like Turbo Max. It is 99% efficient, and only requires a boiler water temperature roughly 10 degrees F hotter than the target DHW temperature.



ME

Ironman

ECM and Aquastat

Try using the aquastat and breaking the "W" wire that goes to the motor through its contacts. Should work as long as the t'stat is setup for conventional heat and "G" is not energized during a heat call. You would still let "W" bring in the pump relay without going through the aquastat.