Temperamental aquastat? EK SYSTEM 2000

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Old 02-05-13, 09:10 PM
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Temperamental aquastat? EK SYSTEM 2000

For the past couple of days the fan/blower on my heating system has not been clicking on automatically when the furnace is heating. The only way to get the fan to turn on is to manually change the fan setting on the thermostat from 'auto' to 'on'.

I called out my oil/furnace service company who initially advised the thermostat (Nest) was at fault, however after he tightened a few wires the blower seemed to start working on auto mode. 12 hours later the fan stopped working again. To rule out the thermostat I swapped out the Nest thermostat for our old programmable thermostat however the fan still was not working on auto. And now, 3 hours later the fan seems to be working again on auto.

I am assuming this could be a faulty aquastat, but would appreciate any advice on how to confirm this. The aquastat is the Honeywell L4008B, temperature set to 140 and the differential set to 15. I have seen the blower automatically turning off when the furnace is on and it's temperature (from the gauge on the front) is at 140+.

Ideas?

Thanks!
 

Last edited by NJT; 02-06-13 at 09:47 AM.
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Old 02-05-13, 11:40 PM
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I deduce from your post that you have what is commonly called a "hydro-air" system where you have a hot water boiler (or perhaps a domestic water heater) supplying hot water to a fan-coil unit or air handler.

Please don'[t be so chary with information on YOUR system. No one here can see what you see and no one here is adept at long-distance (or even short-distance) mind reading. Please give a complete rundown on your equipment along with manufacturer and model numbers of the various equipment. A couple of dozen photographs won't hurt as long as they are well-lit and in focus.
 
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Old 02-06-13, 08:46 AM
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Hi,

Sorry for the lack of information; I'm a newbie homeowner and I don't know a great deal about HVAC systems.

From looking around in my furnace room I have 3 zone oil fired 'System 2000' furnace; zone 1 being forced air and zones 2 and 3 base board. I have attached some pictures.

Thanks.
 
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Old 02-06-13, 09:52 AM
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Matt, I've edited your post title in order to attract some more attention...

However, I don't think you are looking at a problem with the boiler itself...

To clarify, you are talking about the BLOWER MOTOR (fan) inside your AIR HANDLER unit. Is that correct?

Is it possible that the BLOWER is not turning on because the water going to the coil is not hot enough? It must reach the setpoint of the aquastat on the air handler before the blower will turn on.

I don't think the tech was following the proper diagnosis path.
 
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Old 02-06-13, 11:00 AM
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Yes I am talking about the blower motor on the air handler. The furnace seems to be fine and the other zones are working (Base board) as expected.

I believe the water going to the coil is hot enough; if I rotate the temp setting on the aquastat I can hear it clicking when I go above or below the approximate temp shown on the furnace. I would have thought this clicking would have triggered the blower to come on or off but it did not.
 
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Old 02-06-13, 02:21 PM
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I would have thought this clicking would have triggered the blower to come on or off but it did not.
I believe you are correct.

What needs to be determined now is where the voltage is being 'lost'. There should be 120VAC feed going to that aquastat. When the aquastat switches on, of course the blower should power up.

A few voltage checks should determine whether the problem is with the aquastat, or with the blower, or possibly even the power to the aquastat.

Do you own a voltmeter and are you NOT afraid of 120VAC ?
 
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Old 02-07-13, 06:46 AM
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The voltage at the aquastat would be 24VAC. It should be wired to a relay inside the air handler to power the motor. Hearing the aquastat click when you turn it up and down is usually a good indication that it's working. You can jumper it to verify that. One thing I can't see from the pictures is whether the zone valve is 2 or 4 wire. Quite often with hydroair a 4 wire valve is used with the end switch wired in series with the aquastat. If the end switch goes bad it will not signal the fan to start.
 
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Old 02-07-13, 08:03 AM
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Good catch heatpro... looking more closely at the pic of the aquastat one can see that there is low voltage wiring to it. It most definitely is operating on 24VAC.
 

Last edited by NJT; 02-07-13 at 08:21 AM.
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Old 02-07-13, 06:08 PM
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Hi,

Thanks for the replies so far. Unfortunately I do not own a volt meter; I will grab one from the store when this pesky storm is all over. When I do get it what should I be checking? I've uploaded a better picture of the aquastat which might be of help.

Also, frustratingly, the damn thing has been working perfectly since Tuesday night. Weird.
 
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Old 02-07-13, 06:47 PM
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When I do get it what should I be checking?
Without a full understanding of where the wires are going, what they are doing, etc, it's going to be difficult for us to know what to tell you to check!

Would it be possible for you to trace out the wires and draw and post a simple diagram? Even a rough one might give us enough to go on.

What's the make/model of the air handler?
 
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Old 02-07-13, 06:53 PM
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I would start by removing each of those wirenuts and carefully examining the connections. If that's solid wire, sometimes the wires break just inside the end of the insulation jacket. Most often because the guy that stripped them 'nicked' the wire when doing so.

One easy check would be to measure directly across the two terminals on the aquastat.

When the aquastat is calling for the blower to run, you should see ZERO volts across them, and vice versa when it is NOT calling for the blower to run you should see 24VAC.
 
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Old 02-07-13, 07:19 PM
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Does this photo help?

Thanks.
 
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Old 02-07-13, 09:08 PM
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Some of those letters are weird... at first I thought it was

36XHBXR-3HH

But now after looking at the website I think it's

36XMBXR-3HW

and this MIGHT be the closest PDF on their website:

http://www.firstco.com/documents/documents/MBXR-HW.pdf

But, I can't find reference to the "X" after the 36, and before the MBXR.

Does this air handler also do COOLING?

Is it a MULTI-SPEED fan? (I believe that this is a 3 speed fan unit)

I'm beginning to think that you have a BAD START CAPACITOR on the motor... not wiring, not controls, but just a bad part.
 
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Old 02-08-13, 01:32 PM
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Yes, I think it's that one - it does do cooling as well.

What I don't get, and what originally lead me to believe it was the aquastat, is that I can turn the blower of and on 100% faultlessly through the thermostat fan off and on setting; it's when the thermostat is on auto fan mode that it's not working correctly.
 
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Old 02-08-13, 03:49 PM
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Hmmm... I wrote a reply to this earlier! wonder what happened to it? Mystery...

Anyway, here's what I think is happening:

When you switch your thermostat to MANUAL FAN, it is turning on the fan on HIGH speed using the lower of the two relay in the control box for the air handler (see schematic on page 4 of the manual I linked to).

When the thermostat is on AUTO FAN, it is operating off the HEATING circuit and it's associated relay, which is the UPPER one in the schematic.

It MAY be a problem with the thermostat itself, but it also MAY be the upper relay in the schematic (my belief). There is also a slight possibility that there is a loose wire somewhere in the control chain, or a problem with the motor on the low speed winding.

A bit more...

When your thermostat calls for heat, it 'makes' contact on the wires that go to the W and R terminals. This is what activates the upper relay and runs the blower at a different (slower) speed for heating (RED wire to blower motor)

When the thermostat is called for MANUAL FAN, OR for COOLING, the contacts from G to R are 'made', and this operates the lower relay to run the fan on high speed. (BLACK wire to blower motor)

In order to troubleshoot and verify this, one would need a multimeter and the knowledge to read schematics, and know how to safely measure 120VAC circuits.

OR... replace that relay and see what happens, it's probably not more than $20 or so.
 
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Old 02-08-13, 04:29 PM
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I don't have much hope that this will be readable after the forum resizes it but hopefully it will be readable and illustrate what I said in previous post. I'm made notes all over it:

This schematic does not show the aquastat. I believe that you will find it to be wired in series with the "W" wire from the thermostat. In other words, the W wire from the air handler will go to one terminal on the aquastat, the other terminal on the aquastat will get a wire to the thermostat and one to the zone valve.

Can you trace the wiring?

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Old 02-09-13, 12:32 PM
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Thanks so much for that!

One new piece of information which may hopefully be able to help you confirm or reject your hypothesis:

I just changed the thermostat back to The Nest (which I swapped out earlier in the week to make sure that wasn't the problem) - after connecting all the wires it was giving me the error message that the Rh and Rc wires were not connected correctly. I restripped the wires and re-connected and still the same problem. The Nest is now dead, which I assume because it's not getting any/enough voltage from either of those 2 wires.

Thoughts?
 
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Old 02-09-13, 03:18 PM
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I hope you didn't actually 'fry' the bird's nest.

I've not used or seen the NEST thermostat, but what I'm hearing from the pros who have, they aren't overly enthusiastic about them. Seems that they feel that it isn't quite ready for 'prime time' yet. No specifics to go with the anecdotes though.

You really need to trace out those wires and draw some kind of diagram...

Tell us if the wires exiting the air handler match the colors on the diagram, where each of the brown cables in the air handler pic are going, etc... etc...

And, how the thermostat is wired... how many wires, and to what are they connected...

It's really the only way we will make any sense of this at all.
 
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