Aquastat temp not equal boiler temp

scrook_2

1. THIS IS BAD! get the burner & oil filter serviced/tuned up ASAP, it should NOT be tripping the primary, EVER, unless something's wrong -- could be burner settings, nozzle, ignition, chimney draft, fuel, lint/dust in the burner airways, fuel filter, fuel line, fuel pump, motor coupling, motor, or other. Don't keep pushing the reset button!

2. Could be an aquastat problem, could be the sensor's not seated in the well, could be the thermometer on the gauge is off, could be poor circulation thru the boiler, could be something else -- get it checked/fixed when they tune the burner & resolve #1

3. If recovery's only 1 degree/hour don't set back as much, make sure the radiators (or piping) are not airbound, burner's firing at intended rate, circulators are working, baseboards (or in wall convecters) are not full of dust & have free airflow in bottom and out top, piping near boiler & in unheated spaces is insulated, etc. Have the service guy look at these too after he fixes the burner trip issue.

4. look for air infiltration and/or lack of building insulation and seal/insulate to reduce the structure's heat losses further

How much history do you have w/ the house/system?

Carolinas might be nicer than Florida (fewer alligators too), but Vermont's hard to beat!

Tom in VT

Aquastat not equal boiler temp; burner requires daily reset

I'm a homeowner with a 10 yr old oil fired Weil Mclain boiler in a hydronic system with a coil for DHW. Located in Vermont, very cold lately. Did a lot of searching first, and learned much on the Wall and I am trying not to annoy you with FAQ. I really appreciate your help and advice.

Problem number one: 2000 sf house circa 1977 taking about 1 hour per degree to raise from night setting of 58 to daytime setting of 65 at zero degrees outside.

Problem number two: Frequently find the burner off in the morning, reset switch on the relay housing at the oil pump motor having broken the power supply to the burner. Nighttime setting 58 degrees, daytime setting 65 degrees. But the burner is shutting off sometime in the night, so sometimes the temp in the house is down to 52. Takes all day to recover.

Problem number three: In an effort to solve the above, I reset the Honeywell triple Aquastat to 200* hi, 180* low, 15* diff. Observed a few cycles. To my horror, the boiler temp gauge runs up as high as 225* before shut off, then heat soaks up to 235* or so. Pressure reads okay about 20 psi, and no relief valve action so I guess I'm not making steam in there yet . Suspected a faulty gauge so zip-tied the thermocouple of my digital multimeter on the output plumbing as close to the gauge location as possible, and the readings are reasonably close to the gauge readings (within 5*), so think gauge is good.

Here are my questions:

Does the 25* difference between the aquastat hi setting and the gauge reading at shut off indicate that the aquastat is bad, or is this explained because the aquastat samples in a cooler region of the boiler?

Assuming my gauge is good, is it advisable to let the boiler temp run to 225 and drift to 235?

I'm tempted to reset the aquastat hi limit to 200* according to the gauge, disregarding whatever the aquastat dial says. Then set the low limit at 20* below that. Any comments on this strategy?

Or should I just move to Florida?

Thanks very much.

Home Depot Employee

South

It's not the alligators that you need to worry about, they like to mind their own business and stay away from people.

It's the crocidiles that usually get ya and get mislabeled as a allie

Tom in VT

What trips the primary? Big setback?

Thanks scrook for underscoring the importance of the tripping primary. And thanks for the list of possible causes. Could aquastat settings or the large nighttime setback cause tripping?

Unit received its annual in December and passed with high efficiency. Work order and job ticket indicates that filter and line were serviced, air vents cleaned, etc. Tech reset the aquastat. Cold showers and burner trips started after that.

I was trying to avoid another service call by doing a little trouble shooting myself.

You asked about my experience with this 1993 Weil McLain model 68 rated 151,000 btu. Owned the house four years, unit has always struggled to keep this 2000 sf cape built 1977 comfortable on zero degree or colder days. I recall two or three resets required last winter, but now its every other day. THe primary tripping problem seems somehow related to the large nighttime setback. Does this make any sense or seem familiar to anybody?

Weezbo

it sounds ....

like it needed a tune up and cleaning. the high limits been adjusted too much ,when the boiler shuts off and the zones are satisfied the temps rise because like radiant heating stopping the burner is not = with stopping the heat.

if you are pulling water out of a coil in your boiler, and it is winter you can use the tri aquastats coil sensor to run the boiler.