Boiler 3-way valve

bauer

Hi All - 

Forgive the brevity of my post, I am in the truck just writing on my phone, I can update more details when I get home as needed…

long story short, well-McClain boiler with domestic HW coil, I think I’m having trouble with the three way valve. The valve is located in the return lines from the two zones, right before the circulator. 

Upon a call for heat, the valve opens briefly then shuts again, preventing any return water from the baseboards back to the circulator, so I get no heat. Water is hot but just circulates through the domestic coil. 

Unsure if related but I also noticed the circulator is running constantly, even when no call for heat and when domestic coil is well within low/high limit temp. 

I tried a new 3 way valve to no avail, believe it’s a wiring, board or relay issue? In the meantime I manually set the valve halfway open to somewhat appease both the calls for heat and hot water…

Any thoughts much appreciated…

EBEBRATT-Ed

2 zones so you have 1 heating zone and 1 zone for domestic hot water an indirect zone? need more information and pictures

bauer

Two heating zones (1st and 2nd floor hot water baseboard) 

one domestic tankless coil in the boiler. 

Attaching picture of 3 way valve and wiring diagram. 

jpulls11

Sounds dumb. However, there are a series 1&2 of these boilers. When they changed the series number they didn’t change the install instructions right away. The three way could have been installed backwards by mistake. I’m guilty of that once. I’ve also seen the internal plastic guts crumble. Finally it could just be the power head. Lots of ways to look at it and each time I service that style boiler it makes me mad.

EBEBRATT-Ed

@bauer

Looking at the wiring diagram it looks to me like when the low limit control on the boiler is closed that the valve will be closed (even if the thermostat is calling) not allowing any heat for your zones but will allow the burner to run to make domestic hot water.

Once the boiler comes up to the minimum low limit temperature and if the thermostat calls the valve will open to allow heat to your zones.

bauer

@jpulls11 thanks for the heads up on that; had not realized and I did find the weil-mclain addendum now to their instructions.... it is installed correctly

@EBEBRATT-Ed thank you --- I suppose my next step would be to check that limit control to see if it is stuck closed? Either that or one of the NO contacts in the relay is stuck closed.... the addendum I found has an updated wiring diagram. I'm assuming that could also explain why my circulator is constantly running....

Thanks again I will report back with what I find

jpulls11

@bauer seems like some switch is bad then. I remember the last one I worked on it came from the factory with a stupid high set high/low limit. Like 190 low 210 high. 

bauer

Well chalk this up to me overthinking and not checking the obvious first…. Someone set the boiler max temp lower than the hot water coil low limit… so effectively the low limit was always closed because it’s temp could not be reached, thus closing the three way valve and running the circulator constantly. Restored those settings and all seems to be operating correctly - Thanks for the help 

EBEBRATT-Ed

@bauer

I thought it was a little strange the way Weil Mclain wired that.