Outdoor sensor failure

Joe_121

Homeowner here- mine failed over the summer, not quite a year old. I posted the problem here and was advised to contact HTP and mention the items short life span. At that time there were a number of others who posted stories of failed outdoor sensors- thermistors.
HTP sent me one- on the house.........

Plumbob_3

Outdoor sensor failure

A few months ago I got a no heat call on atwo year old Munchkin. There was a call for heat on the ZVC box but the boiler would not fire. I wire nutted the tt wires and still nothing, bingo wwsd. I disconnected the outdoor sensor and away it went, I got a new sensor put it all back together and away it went. The thing that bothered me was that this was a vacation home sometimes unoccupied for weeks at a time.

Yesterday I got a call on a frozen pipe in another vacation home, 5 years old,{we do many} that had burst and done some damage. It happened to be above the mech room and soaked the controls along with a 705 mixing control. When I got there it was on wwsd reading 78 deg. {It was 20 outside} I ran the sd temp to 90 and it took off.

I haven't tested the outdoor sensor to see if it failed or it was the the product of the 705 getting a bath. I am assuming the former.

Is there something I am missing or is there a way to protect these systems from a failed sensor?

tim smith

earlier sensors did have some premature failure issues

they have changed the design some to fix this I think. Tim

Matt_67

sensor failure

I had a similar experience with an outdoor sensor failure with another control manufacturer.This control had 3 boilers,2 stages each,so it controlled 6 stages of firing rate.It happened in the dead of winter,not a good thing. to have a control with an outdoor sensor that fails and unit does not fire in heating mode is bad engineering.In commmercial applications,most heating valves fail in the open position(electric and pneumatic).So why have a design that when sensor fails,unit does not fire is just asking for trouble.You would think that if sensor failed,that the unit would default to normal operation without the sensor.What about liability of such a product?I know ask everytime that I have a control with an outdoor sensor,what happens when sensor fails?and then do not use that control.

Plumbob_3

sensor

I have been installing Knight boilers the last few years and to my knowledge the sensor will fail in the same manner. Life span and cost of the sensor are not the issues for me it is the thought of heat going down on an unoccupied home.

Here is something I can loose sleep over.

Joe Mattiello

If an outdoor sensor fails any of the Taco add-on controls with outdoor reset default to 32 degrees, and will target the appropriate water temperature to satisfy the load. The display will warn you of a failed sensor with an error message. If the zvc board was calling for heat, and the boiler didn't fire, there has to be some other issue.

jp_2

How do they fail?

simply put, they are resistors.

I do not see why they are failing? must be failing to open?

joe is correct, the boilers logic should go into a fail safe mode. when GM's main car computer failed, there was a "limb home mode" that would keep the car running well enough to make it home or to the repair shop. - thats what i was told long ago, sounds good.

Joe Mattiello

I was just thinking; the sensor should not be installed in a sunny area; If so, the internal temperature will certainly be higher then the outside air temperature. This condition may have been the root cause of your problem. Additionally, the sensor either reads the resistance accurately, or gives you an error message, with no erroneous reading.

m dewolfe

I series mixing valve

A point well taken regarding the taco control. My siding contractor yanked mine off the side of the house. the Heat stayed on and the floors were all toasty. A couple days later I noticed the blinking error LED on my mixing valve and had a little look see as to what the trouble was. Score one more for Taco on superior engineering. Temp sensors are little more than resistors mounted in a housing to protect them from the weather. If on fails yu can always replace it with another brand as long as it is the same resistance....I think the Taco ones are 10k [quote needed here Joe]....

SpeyFitter

Vacation homes

In my opinion vacation homes should have glycol in their heating systems.

Alan(OnVacationInOregon)Forbes

I am perplexed

as well as to outdoor sensor failures. I don't know much about electronics; I imagine a resistor is a relatively simple device and when it gets wet, it fails.

I have noticed that my Viessmann sensors do not fail like my Munchkin sensors. The Europeans have been doing it longer than we have? Are they sealed in some way to prevent failure?

Plumdog_2

one type failure.....

I had one fail because the connections got soaked, and were not waterproof. No resistance meant the boiler thought it was infinitly hot outside, which it was not. Soldered the connections and put shrink tube on, and working great.

Joe_121

Instruction say to mount the sensor on shaded north side of building, which is where I have mine- but it still failed. It's about 6 foot off the ground, about 6 foot below the eaves
If it is like most electronic pieces (solid state) I can't figure out exactly how dampness would cause it to fail. As long as it isn't really submerged.
Heck, there is loads of humidity in the air, so maybe that does it in.