Bosch/FHP model EM028 single stage 2.3 ton heat pump, vertical, top discharge. We have been the owners for 2 years. This is a water cooled system. When the water tower was down and no water was circulating through the heat exchanger causing the system to overheat, the high pressure limit switch did not shut the unit down. We found out the switch was bypassed for no apparent reason because the unit is operating perfectly normal.

When we reconnected the high pressure limit switch, it works just fine and trips as expected at 380-390 PSIG.

The previous owner did not even know the switch was bypassed. She is a very nice lady and has no reason to hide this info. Obviously someone bypassed that switch. What possible reason would they have had to bypass it?

Thanks

 

It sounds like you should find out who has been working on that unit so that you can be sure to never let them touch it again.

Does your unit have a Pete’s plug on the entering and leaving pipes?

I am amazed that the condensate overflow switch isn’t bypassed.

 

We have no service history. Only what's on the boilerplate.

Of course. How else would we be able to put a gauge on it.
Not sure what that has to do with my question but yes, the drain pan has an after-market overflow switch.

So are you saying there is no possible scenario the limit switch would ever need to be bypassed?

Thanks

 

https://www.bosch-climate.us/files/EM_Series_RES_US.pdf

Sadly I have seen many geothermal heat pumps with no Pete’s plugs.
Most companies do not know how to use them.

What is your GPM?
If you are tripping on high pressure The waterflow should be calculated.

I have seen a geothermal that wanted one of the two freeze protection circuits to be cut when antifreeze is used.
I have never cut any limits or freeze protection on a geo.

Most geo units have a factory CO condensate overflow switch connected to the primary drain pan.
I have seen this factory switched bypassed. It would be in the top panel of vertical models but harder to see in horizontal models.

An additional field installed float switch is often installed under the unit but this wouldn’t protect your control board.

 

It is not geothermal, just hydronics to a water tower.
There is no problem with the hydronics flow. The only time it should trip is when the water tower is down for service and there is NO circulation at all. It did not trip which prompted me to diagnose the high pressure limit switch and found out it had been bypassed. Reconnected and it works perfectly.

It is easy to simulate overheating because the hydronics supply and return lines both have a shutoff valve. I cut both valves off, it starts overheating as expected and the limit switch shuts off at the right pressure 380-390 PSIG.

So I am wondering why they would have needed to bypass it in the first place?

 

I have a few high rises that use geo’s with that setup.

No, the limit should never be bypassed.