Slantfin SX150 intermittently won't stop firing

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Old 11-20-12, 09:57 AM
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Slantfin SX150 intermittently won't stop firing

occasionally, my hot water boiler will continue to fire well past the temperature i've set the thermostat to. (e.g. i came home from work to 82 degrees last night, not the 65 it was set to) when this happens i'll manually turn off the power to the boiler, and turn it back on after the house has cooled to a reasonable temperature.

as best i can sort out, it's not burning constantly, but it may only be over heat protection in the boiler proper that's cutting out the flame, as the radiators seem to get FAR hotter than through normal use. (i've not thought to check the water temp when it's happened)

this started last heating season, and i replaced the old mercury thermostat with a bimetal one, as a multi meter seemed to indicate it was a little irregular in it's signal. that seemed to solve the issue, but as it was intermittent it apparently didn't. i can go a week or two with no problems, and then it'll stay hot every time i power it up, or be fine for a day or three. there seems to be no pattern to it and i've let it get fully cold or turned it back on when warmish.

it also *seems* to be loosing water somewhere, as i intermittently (maybe once a week) need to add a little water, but it's also burping out the overpressure when it over heats, so that could be it as i'm not finding any leaks in the house (all exposed pipes other than floor penetrations).

any brilliant notions?
 
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Old 11-20-12, 11:32 AM
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Tell us whether it's oil or gas fired. Also, post several good photos of your system - in focus and not with a cell phone. Step back and take wide-angle pix so we can see how the whole system fits together.

It seems that you have two or more problems. First, read this re: the relief valve lifting - http://www.doityourself.com/forum/bo...sion-tank.html

The thermostat must be calling for heat when the boiler is firing although there is a very slight chance that a gas fuel valve is sticking open. When the boiler seems to be firing too long, with a voltmeter check to see if there is 24-V across the fuel valve (if gas fired). If so, then the problem must be the 'stat; if not, the fuel valve must be sticking open.

Bi-metallic 'stats are not great. Try a solid-state type, preferrably not programable, and set its heat anticipator correctly.

Regarding the too-hot radiators, please tell us the temperature and pressure readings on you boiler gauge, with the boiler hot and when it is cooled. What is the aquastat set at?

If this info doesn't make sense to you, you'll need to seek professional help.
 
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Old 11-20-12, 01:06 PM
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it's natural gas, utility fed. photos will have to be cel phone, as my 8MP camera there is a bit more robust than my 1MP old digital camera i'll get those this eve.

i'll look at the expansion tank, although i note that i seem to have that type, and it was installed horizontally. (i'll include pics)

i'm guessing it's the fuel valve, as the new t-stat seemed to be behaving normally, although i'll find the multimeter and check at the fuel valve rather than at the stat lines. (i checked both at the stat, and at the boiler on them to make sure they didn't have a short)

all of this makes perfect sense, although i hadn't thought to check the aquastat yet.

is unsticking the fuel valve going to be a de-gunking or milling/machining (the sorts of things i can accomplish with a halfway decent machine shop or a bottle of acetone and a q-tip), or more of an buy the part tomorrow afternoon before the holiday kind of operation, or could be either?

(also, thanks much for the quick reply)
 
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Old 11-20-12, 01:40 PM
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is unsticking the fuel valve going to be a de-gunking or milling/machining (the sorts of things i can accomplish with a halfway decent machine shop or a bottle of acetone and a q-tip), or more of an buy the part tomorrow afternoon before the holiday kind of operation, or could be either?
No, don't run out and buy anything yet until we know the problem - a sticking fuel valve, while conceivable, is improbable. And if that were it, the valve would have to be replaced, not monkeyed with - they are kind of like a Swiss watch, except a Swiss watch can't blow up your house

But meanwhile, please answer the questions posed in #2, particularly regarding what seems to be a waterlogged expansion tank.
 
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Old 11-20-12, 02:29 PM
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photos and answers forthcoming this evening (after work).

on the expansion tank, i know that mine is a rounded metal tank ~1' in diameter and the shape of a propane tank, but that it's strapped to the ceiling in a horizontal position. (i'll include pics of that) is that an alternate mounting position, or does that sound like a bad installation, or do i not have a membrane type expansion tank? can i safely assume that if i have a tire air valve it's a bladder type tank, and proceed with that maintenance?
 
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Old 11-20-12, 03:21 PM
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can i safely assume that if i have a tire air valve it's a bladder type tank, and proceed with that maintenance?
Yes. .
 
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Old 11-21-12, 03:56 PM
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ok so i'm having image upload issues, more to follow.

pressure tank had <5psi when tested, brought it up to 12 and it seems to be holding there.
 
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Old 11-21-12, 04:00 PM
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https://plus.google.com/photos/11513...00961374802273

so for some reason i'm not able to upload the rest of the photos here, but they can be found above.

i was getting ~24V in a couple of places, but i'm not certain exactly which connections i should be testing.
 
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Old 11-21-12, 04:40 PM
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Did you fully depressurize the boiler (pressure gauge shows zero) before measuring the tank's pressure and adding air to the expansion tank? If not, you will have to redo it. The pressure in the tank is meaningless unless the boiler itself is fully depressurized. If necessary, please reread the instructions: http://www.doityourself.com/forum/bo...sion-tank.html We need to get this issue resolved before moving on to your other issue(s).

After completing all that, tell us what the boiler gauge says, pressure and temp, when the boiler is both hot and cold.
 
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Old 11-21-12, 04:54 PM
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pressure tank had <5psi when tested, brought it up to 12 and it seems to be holding there.
And you followed the step by step directions in the post that gilmorrie linked in previous post? I ask only because if you did NOT, then you still may not have the correct charge in the tank.

The installation of your tank is very unconventional. It will work... but it is possible that there will be premature failure of that relatively new looking tank due to the fact that air can become trapped in the tank. This trapped air may cause premature rusting out of the tank from the inside... but don't worry about that just yet, get the system working correctly first.

gilmorrie said, and we still need these answers:

Regarding the too-hot radiators, please tell us the temperature and pressure readings on you boiler gauge, with the boiler hot and when it is cooled. What is the aquastat set at?
What is the silver dial set to?



Show us a close up of the gauge on the front of the boiler in this pic:



Has your relief valve stopped spewing into that bucket since you charged the expansion tank?

i was getting ~24V in a couple of places, but i'm not certain exactly which connections i should be testing.


In this picture, it appears that the easiest place to measure the voltage to the gas valve is on the ignitor assembly itself.

With the meter set for AC Volts, push one probe into the back of the connector to contact the pin labeled MV/PV (white wire).

When the PILOT is lit, you should see 24VAC between MV/PV and PV.

When the MAIN burner is lit you should see 24VAC between MV/PV and MV.

You will need to 'catch' the boiler when it is misbehaving though... if the problem is intermittent you might have a helluva time doing so.

Basically, if the thermostats are NOT calling for heat and you find the main burner cycling on and off, then we will need to backtrack and find the problem.

It could be :

1. defective thermostat.

2. shorted thermostat wiring.

3. defective zone valve sticking open.

4. shorted zone valve wiring.

5. sticking relay in the aquastat.

6. ? maybe something else I haven't thought of.
 
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