WeilMcLain WM97+ - Temp Rise Too Quickly Lockout

indigo

Hello - had a WM97+ installed about a year ago along with its paired AquaLogic DHW indirect heater.

Issue I am having is that when transitioning from making dhw to then heating the house (single zone) it is locking out with return water registering as hotter than supply water. This issue seems to mostly occur when it's not all that cold out and the water in the house rads is not all that hot. It will then lockout for a couple minutes and reset itself.

I have increased pre and post pump times on both the house zone and the dhw zone, but that does not seem to have made a difference.

Here's an example from one of the error logs, they are flagged as occurring in "Domestic Mode":

Temperatures:
Boiler Out 1: 118F
Boiler Out 2: 117F
Boiler In: 126F
Flue1: 126F
Flue2: 125F
Outdoor: 44F
CWH Tank Top: 150F
CWH Tank Bottom: 138F

Outputs:
Gas Valve: On
Boiler Circulator: Off
Circulator 1: On
Circ 2: Off
Circ 3: Off
Blower Signal: 25%
Alarm: Off

Inputs:
In1: On
In2: On
In3: Off
Manual Limit: Closed
Auto Limit: Closed
Low Water Cutoff: Closed
Blower Tach: 5340RPM
Flame Signal: 0

From what I've read this seems to be linked to a lack of water circulation - as far as I can tell the plumbing is ok, and matches what's in the manual, though it meanders a bit because the space is tight. Is this a matter of increasing zone 1 circulator speed? It's a 3 speed grundfos, which is in its middle position. The system is a dead simple single zone, single zone circulator + boiler circ + dhw circ on its priority zone.

What I believe to be happening is that in transitioning from making hot dhw to main heating water from the dhw loop is entering into the stream and is hitting the return temp sensor thus tripping it - though I really don't know.

I have brought this to my contractor's attention, and they changed the position of the internal primary/secondary bypass valve to closed, which seems logical based on the diagrams, but looking for some additional perspective as it's still tripping.

The house is all cast iron rads with the original plumbing for it all.

Thanks!

njtommy

Could Bad return water sensor and or check all your connections/ plugs. I've seen this several times.
Keep an eye out on your sensors watch the read outs see if you see any extreme changes.

Ironman

If the indirect is close to the boiler, I would shut the post purge off. The indirect is high mass, the boiler low. You're probably pulling heat back out of the indirect, leaving the heat exchanger hot. When the boiler switches over to space heating with its heat exchanger full of hot water and the weather is mild, the ODR is looking for cooler water than what's in the boiler. Thus, the error code. That would be my first guess based upon your info.

IDK why there's a by pressure bypass on your system, but IF it's necessary, it shouldn't be closed off.

Can you post some pics of the boiler and it's near piping?

indigo

Ironman said:

IDK why there's a by pressure bypass on your system, but IF it's necessary, it shouldn't be closed off.

So the valve that was closed during the last service was the internal primary/secondary bypass valve. On the one hand this seems to make sense based on the diagrams as it impedes the ability for water returning to the boiler to mix with water leaving - however, it the manual also states that it should be closed when using only the internal boiler circulator as the main system circulator, else the head pressure from both pumps may be too high. I don't really know what's correct.

indigo

Pictures attached - is kind of squeeze where it is. Indirect tank is built-in to the bottom part boiler the boiler itself.

daveoo

I had a similar issue. The company talked me threw lowering the btu%. I know it's not the correct terms. Give them a call.

Ironman

The only time that the valve should be closed would be IF the boiler circ was also serving as the system/house circ. In all likelihood, since there's so little head from the large gravity flow piping, it could have been piped directly to the boiler without the need for p/s. Since you have an external system circ, the valve should be opened to provide hydraulic separation between the boiler and the system.

Jean-David Beyer

I wondered about this with my Ultra 3 boiler that is very similar, but not identical to the WM97.

Default Prepump setting for DHW is 20 seconds
Default Postpump setting for DHW is 30 seconds

I normally supply 190F to the indirect, and no more than 130F to the radiant slab. So if the slab is cold and is returning 80F water and the Indirect is returning 160F, I worry about a couple of things, though neither has happened.

1.) I have an aquastat on the slab so I do not put excessively hot water into the slab. If the DHW stops and the slab wants heat, the aquastat would see the return water from the indirect zt 160F and shut down the boiler for a while. And I do not want that.

2.) I do not want the "Return temperature exceeds the supply temperature" message, though I have never seen it.

What I do is increase the Postpump setting for DHW to 120 seconds so that the return temperature from the Indirect drops to approach the stored water temperature that runs between 140f and 160F. This allows the water from the boiler to drop in temperature before driving the slab.

Not that the original error message is explained (for the Ultra 3, but I assume the WM 97 is similar is as follows

Condition
Occurs when a return water temperature is greater than the corresponding supply temperature by 10F or more.
Applies to system sensors or boiler sensors.
Condition must occur for 10 minutes for system sensors.

This automatically resets when the condition clears.
System sensors may need to be located further away from the boiler loop connection to the system if proximity to the boiler loop is causing sensors to be heated inaccurately.

Heat_n_CT

I have a Lochinvar WHN with the Grundfos 15-58 3 SP pump that should be run in SP1 for my setup. After about a month from install when it would switch-over from DHW to house heating the pump wouldn't run if in SP1, which would cause boiler temp spikes and lockout. It ran fine in SP2 and SP3. One tech's solution was leaving it in SP2 since it "fixed" it. When I finally had another pump installed that tech checked and there was no juice flowing thru the pump on SP1...new pump fixed it all, been great since that change.

I may be speaking as an uneducated homeowner, but I hope I can get an ECM pump that can use the boiler's 0-10v variability because even on SP1 with the 15-58 I'm over pumping the boiler.

SWEI

Heat_n_CT said:

I hope I can get an ECM pump that can use the boiler's 0-10v variability because even on SP1 with the 15-58 I'm over pumping the boiler.

I've been hoping for one of those for about ten years now.

What size is the WHN?

Heat_n_CT

WHN055. I've read the Taco VVF4-006 could work. But between pump cost and install - Yikes!!

Danscrew

Try turning the internal pump to on low speed and secondary valve open ?

pawel84

Did you ever solve the problem? I have the same issue.