Honeywell Aquastat problems

Ken Gordon

The high limit switch on the honeywell aquastat does not shut off the burner (gas valve) when it water temp. reach high limit setting (160*).
I started having problems with the boiler cycling like crazy then shutting down or continuing to run on. Any ideas? Can the high limit switch/sensor be replaced or would the entire aquastat relay need replacing?

Ken Gordon

can the sensing bulb that controls the high limit switch go bad and start to oscilate?

realolman

I would say

that anything is possible, even if it's impossible.

Why don't you post some more of your symptoms, and I bet someone'll know something.

Paul Rohrs_4

I just changed out a H-well aquastat

on a NEW Peerless MI series boiler. I had the aquastat (operating control) set at 210F and the it would shut off at 190F. I changed it out and the new aquastat ran up to 210F and shut off. I have not seen sensitivity issues up til now.

Regards,

PR

bill_105

Strange days indeed

A few days ago I had a talk with a contractor friend concerning thermal conductive paste supplied with aquastats. Topic was left wide open. Later that day I spoke with the the heating control guru of our very north state. They say don't use it because boilers here run so hot and it's pointless. Perhaps there is a different reason. Does this stuff really matter.

realolman

What

is the model number?

realolman

I can't

see what it would hurt.

My understanding is that the bulb doesn't fit as well in the well as it might, and that the paste will fill the voids and conduct heat from the water to the bulb better than the air in the voids would.

Practically, I really can't see it making much difference one way or another.

Unknown

I have found that the thermal conductive paste makes a difference in how fast the aquastat responds to a change in temp. The paste allows better transfer of heat from the well to the sensing bulb. Without the paste I notice more overshoot of the boiler water temp over the aquastat setting.

When using a strap-on aquastat mounted to a pipe, I notice a big improvement in accuracy and response time when some paste is applied between the sensing bulb and the pipe.

realolman

You're probably

right... They make it for some reason.

rich pickering

If no thermal paste...

If the he thermally conductive paste was NOT used, and the bulb shifted, even slightly, in the sensor well it is quite possible you'd see overshoots, and perhaps undershoots on the other end, in temperature. Use the thermal paste! It helps the probe to more closely follow the temperature of the water.

A.J.

Conductive grease

F.Y.I. if you use the heat conducting grease plan on changing out the well if you ever go to change the aquastat. t will act like cement and your capillary tube will break off long before you sensing bulb will coe loose.
We do see wide range of temp. on H. W. aquastats.

Unknown

Heat transfer grease

if you have noticed is not used when systems are new. It is shipped with replacement aquastats. Its purpose is to increase sensitivity to heat in the boiler water as the well on the water side becomes some what insensitive to temperature due to corrosion and becoming caoted with a film. In the past the grease had a drying agent added which caused it to end up like cement. I was told when I was with Honeywell from 1994 to 1999 that all new heat transfer compound no longer has drying agent added and should not harden up anymore.