need help with a Utica boiler MGB150HD safety switch

John_188

I've a mgb150hd utica boiler where the pilot is on but the unit does not fire up. I have cleaned the system professionaly,replace the coupler line, and the only way it fires up is by hitting the reset button. the heat comes on then when the temp declines the unit does restart to provide heat. any ideas??? thank you in advance!!

Mitch_4

Is the reset

on the flame roll out safety switch? If so, make sure the bracket that holds it is straight up and down, the safety should not be in the hole to the burner compartment. There should be a space.

As the burner fires, air is drawn in around the switch, keeping it cool enough to not trip. But if there is roll out, the flame exits the hole, trips the safety. Sometimes during service the bracket gets bent out of position allowing the switch to see the radiant heat from the flame and causes nuissance lockouts.

If the bracket is ok, then get the pro that cleaned it back..sounds like you have an unsafe condition and the safety is doing EXACTLY what it is supposed to, or a defective switch

(been there done that, had to fix it under warranty..that is how I know)

John_188

ironically i replace this switch last year and wonder if this could be defective again? the switch is straddle on bracket with the round face switch facing inward into the chamber. are you suggesting back off the bracket so that it is less inside the furnance chamber?

Mitch_4

no..

but the bracket should be be straight up and down, and not bent towards the opening. (The face of the switch is paralell to the hole, with an equal and even space at the top and bottom.

When you screwed the new switch in, you may have bent the bracket..

Mitch

Glenn Sossin_2

Sounds like a draft issue

How tall is your chimney? Is this a relatively new boiler install? Is this boiler larger than the one you had? What size is your chimney? Is it clean? Does it have a liner? Did your professional inspect it? Sounds like a draft issue.

You have an atmospheric boiler. This means it removes flue gasses by convection - hot air lighter than cold air. When your boiler starts up, there is minimal draft. If there is insufficient draft, or even a downward draft, the blocked vent switch (BVS) may trip because the flue exhaust doesn't travel up the chimney. There may be negative draft effects, i.e. windy day/evening creating a condition where the BVS is tripped. If it is chimney related, I'd make sure you have a CO detector located in the boiler room.

I agree with Mitch, the switch sound like it is doing what it was intended to do. The question is, why don't you have sufficient draft? When was the last time your chimney was checked? It could be a bad switch too but I'll bet on a draft issue.

The cold weather is starting to bring out the animals like raccoons and squirrels. They may start building a nest in your chimney in between warm and cool days when there is a long length of time between firing.

I had to change out my sisters water heater a few months ago, just happen to look in the chimney piping to confirm it was clear, and found 2 fried squirrels.

Check out your chimney. Be sure there are no obstructions that could impede a satisfactory draft from being established.