Burnham Alpine Boiler Pump Runs with DHW Priority

[Joe123]

I installed an Alpine 105 boiler for my new staple-up hodronic system. The boiler has three pumps, boiler, system and DHW. The system and DHW pumps are connected to the Caleffi relay box. The boiler pump is connected to the boiler. With the boiler configured for Central Heat - Optional Priority the boiler pump should not run when there is a priority call for DHW. However, both the boiler and DHW pumps run at the same time when there is a priority call. Since I have different set points for my heat and DHW, this could cause some issues, but I also think that I'm getting some back pressure from the boiler pump, which is reducing the flow for the DHW piping.

I hope this makes sense. Does anyone know why the boiler pump would be running in this configuration? Any way to make it not run when there is a call for DHW? Thanks in advance.
Joe

 

[Tom Sawyer]

The boiler pump always runs on any call for heat or hot water

 

[Sponsor]

 

[Joe123]

The boiler pump always runs on any call for heat or hot water

This is from the Burnham manual. I'm I reading this wrong?

"Central heat, Optional Priority: Pump Runs during central heat and frost protection call for heat. Pump
does not start for a DHW call for heat and will be forced off if there is a DHW call for heat and Domestic Hot Water Priority is active."

 

[Mage182]

Since the water in the primary loop is considered to be in the boiler, that water needs to be moving whenever the unit is running. This is compensation for the unit having such a small heat exchanger. If you don't run the boiler pump for any call the zone pumps may not be able to move enough water through the system on their own and the water in the heat exchanger will boil.

 

[Joe123]

Since the water in the primary loop is considered to be in the boiler, that water needs to be moving whenever the unit is running. This is compensation for the unit having such a small heat exchanger. If you don't run the boiler pump for any call the zone pumps may not be able to move enough water through the system on their own and the water in the heat exchanger will boil.

Thanks for the reply. The DHW loop has a separate loop and dedicated pump to the boiler, so the 'boiler' pump is not necessary when the DHW pump is running. I believe that is the intention of the 'optional priority' pump configuration. I just don't understand why it's not working as descripted.

I tried to upload a PDF of my piping diagram but apparently a 400K file is too large.

Thanks,
Joe

 

[Mage182]

What size tank are you running?

 

[Joe123]

What size tank are you running?

I called Burnham tech support and they were very helpful. Turns out there are two pump settings, one for the system pump and one for the boiler pump. I had adjusted the system pump but failed to look at the boiler pump. I'm confident that this will resolve the issue. Thanks for everyone's help.
Joe