Weil McLain CGA boiler protection

BrianF

New boiler being installed on a converted gravity system. The original coal boiler is long gone and there is currently an oversized circa 1980 Peerless gas boiler. It’s piped in direct with a 007 on a fairly large system. The system works great and the house heats nearly perfectly.  Anyway the low temp has probably taken its toll as the boiler is toast. 

Weil McLain calls for primary secondary piping for this application. Then they want you to throttle the valves (7a & 7b) to provide an acceptable return temperature. Is this acceptable?  

Would it be better to use their piping and install an aquastat to kill the primary pump when the return temperature drops?  I feel like doing that is going to give uneven heating if the pump isn’t running for a consistent long period on a gravity system. That old boiler would do 20-30 minute cycles and probably has never went over 120 degrees. 

I know the boiler protection valve is probably best but is their way okay?  

EdTheHeaterMan

Caleffi has a boiler protection valve made just for that purpose. @hot_rod will chime in here soon to explain it. https://www.supplyhouse.com/Caleffi-280176A-1-1-4-Female-NPT-ThermoProtec-Thermostatic-Mixing-Valve-140-Degrees-F-Tset
Read full article here: https://idronics.caleffi.com/article/32/5-righting-some-wrongs

BrianF

That valve is certainly the best way to do it. However will it work and is their a down side to doing it as to the manufactures specs with gate valves?  It’s a simpler concept with no mixing valve to periodically repair. 

EdTheHeaterMan

The down side it that there is no way to completely uncouple the cold return water from the boiler return during start up. the boiler will receive a fixed amount of bypass and a fixed amount of system return from system with the manual valve setup. There is no way to increase the boiler temperature for the start up period. and during the fringe seasons (Spring and Fall) the boiler may not operate long enough to reach the desired temperature to eliminate the condensation.

The Mixing valve will completely uncouple (not let any return from the radiators) the system until the boiler temperature can sustain the minimum temperature for eliminating flue gas condensation. That may take 3 to 4 minutes with the mixing valve. With the manual valve design, that could take 8 to 10 minutes or more, before the return could be at the 130° or 140° recommended temperature. And in the fringe seasons you may only get 6 or 7 minute cycles until the thermostat is satisfied.

But in the dead of winter, when the boiler is on more than it is off, you will see little difference.

realliveplumber

Weil Mclain should take that valve arrangement section out of their manuals.

They're never set properly. as soon as someone sees a valve open 1/2 way, they instantly either open it or close it.

It doesn't work well anyway.

The Caleffi valve listed, orthe Danfoss ESBE is the way to do it correctly.

BrianF

I was actually wrong and must’ve got that picture from an old book after I had already seen a newer one. Weil McLean did take that setup out of their book. I didn’t notice the lack of the primary secondary setup in the picture I posted. This is the way they show it now.

EdTheHeaterMan

Still like the mixing valve idea. Although I did not install them in the past, and I am now retired, there are several boilers I have installed with condensation in the flue gas problems that I piped using the manufacturers suggested piping. It's too bad that we need to make the mistakes and discover them years later to learn the correct (or better) way to do things.

But that is the way of life!

realliveplumber

They are still showing 7a as a "system temperature valve"

Thats not a good way to provide boiler protection.

hot_rod

The problem with a fixed setting valve is that it is set for only  one specific condition

If you set it at cold start, as the system warms, it will be bypassing too much flow  You may never get the SWT you need

primary secondary piping is not a fix either. It doesn’t have temperature sensing