Heat & hot water problem PLEASE HELP

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Old 01-09-07, 06:50 AM
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Heat & hot water problem PLEASE HELP

Hi everyone,
Ok first off I have a slant/fin gas boiler with forced hot water baseboard heat. It has 3 zones one for the up stairs one for the downstairs and one for the hot water. My hot water tank is heated from the boiler it doesn't have a pilot. Here is the problem.

First here is how "I believe" the sequence of events to work.
1. One of the thermostats calls for heat and the electric box on the wall I'll call it the thermostat relay box picks the relay for that zone and the LED for that zone lights.
2. The circular pump for that zone turns on.
3. A signal is sent to the exhaust fan to kick on (Here in lies the problem)
4. A vacuum sensor with a metal tube going outside sucks the air back in and tests to make sure the exhaust air is clean.
5. Once it sees clean air it sends a signal to the automatic damper to open.
6. The automatic damper turns open and sends a signal to the boiler to fire.
7. The boiler fires and starts to heat that zone

Ok It seems at times the exhaust fan never kicks on bringing the whole process to a screeching halt. The LED will light for the zone and I can feel the circular pump working But I don't hear the exhaust fan kick on. It happens mostly in the morning aft we have had the heat turned down all night. When it happens we will have no heat or hot water. Usually I can just turn the boiler switch off and on a couple times then give it a minute and the fan will kick one and everything else works after that.

Here is what I have tried so far to try and resolve this problem that has gotten me to this point.

The automatic damper control motor has been replaced.
The Aqua stat relay has been replaced.
The vacuum sensor has been replaced.
I have tried blowing out the metal tube connecting to the vacuum sensor with my compressor in case it was clogged.

Any one who could shead a little more light on the cause of this problem would be a HUGE help!!!!! Thanks in advance
 
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Old 01-09-07, 07:15 AM
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What model is your Slant-Fin boiler?

"thermostat relay = zone controller"

I like your term better... since the t-stats should be the zone conrtroller.
 
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Old 01-09-07, 08:16 AM
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What's the make and model of the "exhaust fan"? It sounds like you are describing a "power venter," in which case it is likely a Field Controls or Tjernlund.

The vacuum thing is also known as the pressure-proving switch. It is basically checking to make sure the air is going up the flue (i.e., sufficient draft) before allowing the boiler to fire. If the boiler fired without adequate draft, then your house could fill with carbon monoxide and you might wind up dead. Not good.

Vent dampers also have a "spill switch" that will also shut down the boiler if it detects insufficient draft.

I'm going to guess that you have a bad pressure-proving switch, or it is in need of adjustment. If it's a Field, surf over to www.fieldcontrols.com and either post a message on their discussion board or call tech support. I used to have a Field power venter and they were very helpful on the board and over the phone.

On second thought, however, on my old system, the vent damper opened first, then the power venter started (i.e., steps 5 and 6 are reversed). This might be the problem if the power venter is trying to prove the draft while sucking against a closed vent damper. Like trying to suck air through a straw with your finger over the end....

This problem gets into an area involving the safety of your system and the health and safety of people. I strongly suggest calling a pro if anything leaves you feeling the least bit uncertain.

While you're doing all this, please be sure you have CO detectors installed on every floor of your house, even/especially the basement. Make sure they are working.
 
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Old 01-09-07, 09:23 AM
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Specs

Here are the models
The boiler Slant/fin Sentry S-90 DP
Switching Relay is Taco SR50 3 3 zone
Vent is field controls CK-40FLN (I replaced the pressure-proving switch just the Switch itself not the whole box) Not sure how to do any adjustments on it.
The Aquastat Relay is Honeywell L8148 E (Replaced)
The Automatic Damper is Johnson Controls M35BC-1 (replaced)

I have had 3 different plumbers in to look at it but by the time they get here is is working fine again that's how I came to replacing these parts. They took their $75 for the visit and left, but I was able to pick their brain while they were here. Only one of them saw it failing and when he played with the tube on the pressure-proving switch the fan would kick on and the damper would open (it kind of happens at the same time) then the boiler would fire. Then he said the pressure-proving switch was the problem so I replaced it. I did not replace the tube itself.
 
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Old 01-09-07, 09:50 AM
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When in doubt, go to the manufacturer. Post a message on the fieldcontrols discussion forum at http://www.fieldcontrols.com/forum/

There's someone there named Lynn Cahoon who's knowledgeable. Although some of the forums haven't had activity in a while, they watch and respond quickly.
 
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Old 01-09-07, 09:56 AM
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Just an FYI

Just thought I should mention a couple other things just in case they are relevant. This is a new house only about 5 years old so all of this equipment is pretty new. Also I have had another problem since day one I don't think has anything to do with this but I figured I would mention it in case maybe someone thinks it does. When the first floor thermostat or the hot water thermostat call for heat even with the 2nd floor thermostat off the baseboard will be luke warm. The circular pump for 2nd floor zone is not on and is cold but the line going into the pump is warm. I have gotten around by shutting off the valve on that pump in the summer then I just keep the heat off upstairs and open the valve in the winter. Just thought I should mention it.
 
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Old 01-09-07, 09:57 AM
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I will check out their forums too thanks.
 
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