Hydrostat Hi limit issue

dirtbike59

Hey I’m using a hydrostat 3250 plus. I noticed about 2 weeks ago my buderus was running and I saw the water temp on the display say 201 and still going. I opened the cover to check the high limit and it was at 209. I’ve never set it there. So I turned it back to 190 and the unit turned off. Now 2 weeks later I just noticed it was at 198. Is the knob creeping due to either vibration or thermo expansion and contraction? Anyone else seen this issue? I am using a OAT but didn’t think that would change the hi limit setting. 

EdTheHeaterMan

You are correct, the vibration is moving the knob. Another reason I prefer Honeywell L7224U.

You could try some painter's tape on the knob to the circuit board. Call the supply house where the boiler was purchased and see it they can offer warranty replacement. Most boiler parts are only 1 year warranty, but you may have extended warranty. Doesn't hurt to ask

MikeAmann

EdTheHeaterMan said:

You are correct, the vibration is moving the knob. Another reason I prefer Honeywell L7224U.

You could try some painter's tape on the knob to the circuit board. Call the supply house where the boiler was purchased and see it they can offer warranty replacement. Most boiler parts are only 1 year warranty, but you may have extended warranty. Doesn't hurt to ask

Without hijacking the OP's thread, ED, what differences make the Resideo 7224U better than the Hydrostat 3250+?
https://www.supplyhouse.com/Resideo-L7224U1002-120-Vac-Oil-Electronic-Aquastat

HVACNUT

I've never used ODR with the 3250 Plus, but I'd assume there's a max limit setting to correspond to the design day. Maybe go through the settings again.
And I've got many many 3250 Plus controls out there, and never had one mysteriously self adjust. 
Maybe a huge delayed ignition could jolt it but...

MikeAmann

HVACNUT said:

I've never used ODR with the 3250 Plus, but I'd assume there's a max limit setting to correspond to the design day. Maybe go through the settings again.
And I've got many many 3250 Plus controls out there, and never had one mysteriously self adjust. 
Maybe a huge delayed ignition could jolt it but...

I did install the ODR sensor, but ODR doesn't work well for my situation, so I have it disabled.
I do like and use the WWSD function.

EdTheHeaterMan

MikeAmann said:

EdTheHeaterMan said:

You are correct, the vibration is moving the knob. Another reason I prefer Honeywell L7224U.

You could try some painter's tape on the knob to the circuit board. Call the supply house where the boiler was purchased and see it they can offer warranty replacement. Most boiler parts are only 1 year warranty, but you may have extended warranty. Doesn't hurt to ask

Without hijacking the OP's thread, ED, what differences make the Resideo 7224U better than the Hydrostat 3250+?
https://www.supplyhouse.com/Resideo-L7224U1002-120-Vac-Oil-Electronic-Aquastat

The Honeywell limit is set by pressing buttons to a particular temperature that is displayed by a three digit display and once selected you save that setting. There is no dial to turn. My first experience with the Hydrostat devices was that the potentiometer dials were inexpensive junk that is soldered to a low cost PC Board. Just did not have the feel of a quality built control.

That was just my first impression. I retired soon after those controls became standard OEM control on many boilers. Just a personal preference. That's all.

Kickstand55

In have a customer that I installed a boiler for with that control. He called me about 2 years after to tell me there's no heat. On arrival I noticed the control locked out on high temp. I reset it with him watching. He's electronics guy, and is inclined to understand these issues. It has happened a couple of times since, so he said. I like the old clunker electro-mechanical controls better, just 'cuz I'm old too.

STEVEusaPA

Kickstand55 said:

In have a customer that I installed a boiler for with that control. He called me about 2 years after to tell me there's no heat. On arrival I noticed the control locked out on high temp. I reset it with him watching. He's electronics guy, and is inclined to understand these issues. It has happened a couple of times since, so he said. I like the old clunker electro-mechanical controls better, just 'cuz I'm old too.

How does it lock out on high limit and need to be reset?
It turns the burner off on high limit, like any aquastat. The circulator runs until the call for heat is satisfied, and the burner comes back on after the temperature drops.
IOW, something else was wrong.