The case of the backward flow, this Friday's case

RayWohlfarth

A customer requested a service call at their newly purchased building. The plant had two boilers and four zones. When we arrived, both boilers were at the set point but the supply pipes were cold. Instead the return pipes were warm. We verified the pumps were working on each boiler and flowing in the proper direction. Thinking it had to be something in common for both boilers, we looked at the piping. The supply pipes from each boiler rose and then fell. We thought it could be an air pocket because there was not air vent. We installed a tee and an air vent but the system did the same thing. The return pipes to each boiler were hot and the supply pipes cold. I will let you know what we found on Friday at 6am EST.

EBEBRATT-Ed

Flow must be backward in the primary loop. The flow is unbalanced somehow. Probably the short primary loop is moving too much water causing backwards flow in the common piping in between the primary loop tees

JUGHNE

Inlet and outlet of boilers is reversed, connected wrong, need to be switched.

Pumps pulling cool water off of the bottom of boiler.

dko

I haven't seen gas piping painted GREEN before

mattmia2

So obviously the boilers aren't piped properly, they should each connect individually with closely spaced tees to the primary loop, not tee together then make one connection to the primary loop.

My guess is that the description is a little off, the supply pipes at the boilers are actually hot and one circulator on one boiler is stronger than the other so the stronger circulator is pulling water backward through the weaker circulator and it is just circulating in a loop in the boiler loop piping.(or the boilers are rotated and one circulator is off and there is no ifc causing the same situation)

The point of primary secondary piping is hydraulic isolation and you lose that isolation when you tee the boilers together in to one boiler loop connection.

I also can't quire see the second tee for the boiler loop connection to the primary loop but i'll assume it is behind the left boiler somewhere.

Of course this brings up the question of how did this ever work. I suppose someone replaced a circulator but after that it would have never worked or when the building is under enough load both boilers are firing and both circulators are running if it is a check valve issue.

mattmia2

Or if they did it the way they did to have the option of adding more boilers they could make a boiler loop with its own circulator that connects with closely spaced tees in to the main loop and connect each boiler with its circulator in to that boiler loop individually with closely spaced tees.

EBEBRATT-Ed

@mattmia2

Actually, they are piped the way they should be piped. If each boiler connects to the primary separately, they will get different return temperatures and if running both boilers one boiler will affect the other boilers temp.

Most manufacturers with multiple boilers will show them that way. You want the boilers to get the same return temp and the supply temps from each should mix before it goes into the primary loop.

mattmia2

Then just missing IFC? Are the boiler pumps wired so they are shutting off when the boiler reaches setpoint?

GGross

That boiler on the right has the knock off resideo pump, not sure if those ones come with the IFC, I do see it as an option to add one though. anybody used those out of the box that might know?

John732

Well first off that’s not a drip leg on gas line lol. Pointless. So what’s the out come?  curious to know after reading every ones comment . I kinda agree with check valve points. Interesting kinda like to learn something from this 

dko

I wasn't familiar with that burnham model so looked it up. In case anyone else isn't familiar with the internals of that unit here's a snapshot

SgtMaj

Kind of making my head hurt, and define hot and cold.

GGross

So the boilers have a p/s loop inside them (technically secondary/secondary?) then connect to a primary loop via close tees, then each zone is piped as a secondary loop off the primary via close tees. The piping diagram from Burnham shows basically this same setup, though without the zones being piped primary secondary it just leaves that primary loop to the imagination, I am thinking the issue lies in the primary loop. I do respect how they market the internal piping as making piping the boilers much simpler and faster, even though it adds extra piping and pumping requirements and makes the whole system a headache to look at.

Kvac13

If the boiler pumps are hooked up to a control that activates them once the boiler reaches a set temp, the water will move up the return from gravity because there is no resistance. All the heat goes out the return and it will take a very long time for the supply line to see the temp it needs to activate the pumps.
Ive seen this happen on dunkirk boilers.

Adk1guy

My guess is G Gross is correct and the piping should be changed to follow the schematic. There is no mention how the system is wired but I'm sure the installation instructions cover it. When all else fails read the instructions.

SgtMaj

Kvac13 said:

If the boiler pumps are hooked up to a control that activates them once the boiler reaches a set temp, the water will move up the return from gravity because there is no resistance. All the heat goes out the return and it will take a very long time for the supply line to see the temp it needs to activate the pumps.
Ive seen this happen on dunkirk boilers.

that was a similar additional thought that I had. but I can't figure out why the zone returns are piped into that primary loop on the wall, doesn't seem very efficient to mix the return water into the feed as it makes its way down the line. Don't the returns need to be piped on the far end of that loop on the wall?

dennisclos

These boilers already have a supply pump in them, looks like return pumps were field added, which may be the problem, as these pumps all working together may overcome the main loop pump ability to circulate correctly.

hot_rod

I think the circ inside those boilers us just for return temperature protection, you still need a boiler pump

they were a nice boiler, an answer to the Weil GV
But they had the early problematic HW smart valves on them

GGross

Yeah the internal pump is not a supply pump, just circulates through an internal boiler loop, still need at least one external pump

bhiggins

They need more and better insulation on those pipes.

rbeck53

When the internal pump or VS3000 fails the hot water will go out the return pipes. If the internal pump fails replace with only standard pumps no ECM's.

RayWohlfarth

Thanks for all the comments, guess, and troubleshooting Well this case humbled me. We thought for sure the piping was air bound and installing the new air vents would solve it. It didnt. I knew the boiler pumps were running and yet no heat on the supply pipe. The problem was the check valve on the pump outlets were frozen and didnt open. I would have never thought both would do that.

gerry gill

Thanks for the lesson Ray

dko

Full of sludge?

SgtMaj

Yep, that would do it.

RayWohlfarth

@gerry gill Most welcome sir
@dko They didnt appear to be full of slide. I pushed in with my screwdriver and they were stuck closed
@SgtMaj I learned a lesson that day. Never assume. I get humbled regularly in this industry LOL

mattmia2

I had that happen with my caleffi prv. It looked like some scale welded the valve to the seat. it kind of seemed the additives to keep the water from leaching copper and lead had deposited on the seat as it sat unused.

John732

Oh wow I was agreeing with earlier post about check valve assuming everything was piped correctly. Never would’ve thought of them stuck closed. Thanks everyone made me think here about things I would have not thought of . I’m still learning things every day 

Adk1guy

Both stuck closed! How bizarre. Seems logical there must be a root cause. Nothing harder to troubleshoot than a coincidence.

RayWohlfarth

@mattmia2 I swear the water company is adding new chemical to the water. Im not sure what caused it but when we replace the other circulator I will try getting some pictures.
@John732 I never would have imagined both were stuck closed. They told me they had heat a few weeks earlier
@Adk1guy I know! If I was placing a bet, I would bet the house on an air pocket in the piping

GrafHeating

"Both stuck closed! How bizarre. Seems logical there must be a root cause. Nothing harder to troubleshoot than a coincidence."

I wonder how many more had this problem I have to keep reminding myself that "quality control" doesn't mean good quality but rather uniform quality.
That is one reason that I have stopped buying case lots of almost everything. The last was a whole string of a particular and very popular zone valve. They would work for a few months and then the end switches would fail. The issues disappeared after my supplier received a new shipment.

RayWohlfarth

@GrafHeating We are seeing lower quality on almost everything we get now. It's sad because the customer equates the poor quality with us. They think we installed it incorrectly