Hot water heating trouble... not sure what to do!

swm5126

So, I'm a fairly new home owner. The home came with a boiler system that is about 12 years old and has been serviced every year. It's a Slantfin Sentinel SE 105 DP. Up until about a week ago, everything was working fine.
In the past few days, this is what has been happening: when the thermostat calls for heat, the boiler comes on - damper opens, pump kicks on and burners ignite. Then after about 10 minutes the burners shut off, but the circulator pump continues to run (because the thermostat is still calling for heat I assume). After about 7-10 minutes the burners come on again. They run for maybe 3 minutes and shut off. This cycle continues until I either turn the thermostat down or the house finally reaches temperature (which even at 50*F right now, it takes forever to get it to go up even a couple degrees, before this issue arose it never had problems even at much lower temperatures).

The water temp reaches between 85-90 degrees eventually, and then never gets hotter. Pipes going into the circulator are warm and the same temp as the gauge indicates(confirmed with infrared thermometer). All of the pipes are the same temp. When it was working previously, the temp would reach 175-180 (and the burner would run the whole time until it reached the temp).

Additionally, the aquastat is a Honeywell 8148e, and it appears to be set to approximately 200*F. I've gone over all the literature for the boiler, and the only seemingly relevant troubleshooting information appears on the auto damper manual. The section states "Symptom: Intermittent burner operation. (Damper operates normally). Possibly causes: Burner access door open/bent or broken coupling/bad ground/damaged or defective switch" As far as I can tell, the damper is operating normally, when the thermostat is calling for heat, it opens. When it's satisfied, it closes. I don't know if this even has anything to do with it, I just thought I would lay out ALL the info I've come across looking into this.

Anyone have any clues as to why the burner isn't letting the water reach the temp it should be at? Could it be a faulty aquastat? I've never had a boiler before so I'm unfamiliar with a lot of it. I just know previously it had been working fine for weeks, and in the end of the last winter when we bought the place. I have a multimeter I know how to use, I'm just not sure what to be checking to figure out what the issue is here.

JUGHNE

Does the tstat have a battery? You might change it to eliminate the simplest fix.
Is the temp gauge you are looking at inserted into the boiler?
What is the pressure if it is a combo gauge?

swm5126

Thermostat is an old round Honeywell, so no battery. Temp gauge is inserted into the boiler, and the temp on it matches my infrared thermometer. PSI is at about 12 when it's running and the water temp is maxed at 100*F. It may have been higher when it was reaching temperature, but I never paid attention to it since it was working.

Mike

Is the vent damper staying open after the burners shut off?

swm5126

Yes, when the burner shuts off it's still open. Only when the thermostat stops calling for heat does it close.

newagedawn

could be a weak thermocouple

JUGHNE

So either some boiler temp control or flame sensor loses its signal and retries again.
Do you know if you have electronic ignition that establishes the pilot light?

swm5126

Like when it heats up it breaks connection?

JUGHNE

First, do you have spark ignition?

swm5126

Not sure on that. I'm pretty sure when the system is off I can hear the pilot light. But when the burners kick on I can hear a buzz sound before they light.

HVACNUT

Is there an ignition module with electric ignition or standing pilot? If it has an ICM. make sure there's a good ground from it to the gas valve.
Also, it might be tedious, but if you can leave your meter on B1, B2 on the aquastat to see if it loses 24v when the burners drop out.

swm5126

I will check those when I get home and double check the kind of ignition.

JUGHNE

A picture of the controls with the front door of the boiler removed would help.

unclejohn

Send a picture of the boiler control and gas valve. The damper should shut if the aqua stat gets to temp. So for some reason your losing the gas valve.

swm5126

The manual for the ignition controls says it's a "continuous pilot combination gas control" so I assume that it's a standing pilot. So I got my multimeter hooked up, on B1 and B2. It seems like it's actually longer in between ignitions now(even since yesterday) and the temp is only barely holding at 90. When the tstat is calling for heat and the burner is on, I get 24.00v. When it shuts down inevitably, it goes to 0.585v. I'll try and post a pic shortly.

swm5126

Here's the aquastat and the gas valve

HVACNUT

Can you get a closer pic of the aquastat? I can't see the dust mite behind the transformer. Ha, I'm hilarious.
But seriously folks, I see your meter connected to the gas valve. You stated you tested at B1, B2 and lost 24v even with a heat demand, so the problem lies from the aquastat back to the thermostat.
Check with the meter at TT on the aquastat. Reading should be 0 with a heat demand. When the flame drops out, the reading should still be 0. If the reading goes to 24v, even for a second, it's the thermostat, or the thermostat wiring (Old wiring).
Is there anything wired in between TT and the thermostat or any splices?
If the the reading remains at 0, then it's the aquastat or vent damper.
There's a little black switch on the damper motor. After you test all from above, if all checks out ok, switch the motor from auto to manual open. That will permanently close the end switch and keep the damper open at all times. If the problem goes away, it's the damper (You can actually try that first, before testing the thermostat circuit).
The fact that the burner circuit consistently drops out at 90 degrees sways me towards a faulty aquastat.
*When we get this resolved, get rid of the mercury thermostat (dispose of properly) and install a digital.

unclejohn

Sounds to me like you have a bad aqua stat. You can try with the boiler calling for heat to lift the armature of the relay and let it slam back a couple times to try and clean the contacts. Other then that supplyhouse.com has your part.

swm5126

When you say check TT, would that be between TV and T on my aquastat? I've attached a picture.

Also, I tried what I assume is the manual bypass on my damper (didn't see a black switch so I took the cover off and followed the directions for emergency operation). I'm not able to move the damper at all when it's in emergency mode like it says (system on and tstat calling for heat). After you switch the wire from A to B it says you should be able to move it until the green light comes on (which does come on when it's opened automatically).

There's also some kind of sensor just under the flue? Not sure what that is.

Sorry the pics aren't great. It's in a tricky spot to get a good pic of the aquastat.

unclejohn

Take a piece of t'stat wire and put one end under the "Z" terminal and the other end under the "B1" terminal. Now you have bypassed the relay and the aqua stat in the honeywell control. If you get water temps above what you have been seeing it's the control. Remove the jumper and replace control. Your diagram is on page 8.

JUGHNE

The sensor under the flue; does it have a red reset button on the bottom? If so that is manual reset and is probably not your problem.
If no reset then it is auto reset......gets too hot and opens......cools down and closes which will turn burner back on.
If you follow those wires they could be in series with other thermo safety switches.......maybe one down near the burners.

Most burner ones today are one time fuse link
Most flue ones today are manual reset

Your system is older and could have different controls.

Your wiring diagram for the boiler might show you what is there.

swm5126

With the thermostat not demanding heat I get a reading of 24v. When I turn it up a bit so it calls for heat, reading across TT is 0.290v. When the flame kicks out, it reads 0.303v.

I'll try jumping the burner later to see if it stays on. Thanks for all the help so far guys!

mikeg2015

I think it's the flame sensor. Has combustion analysis been done. Too much primary or secondary air, or gas pressure off can cause fame issues. Pilot might need adjustment.

My steam boiler was doing this and a few small adjustments and it went away. Too much secondary air I think was causing much of it. My chimney is really tall (~38') so draft was very strong.

HVACNUT

> @swm5126 said:
> With the thermostat not demanding heat I get a reading of 24v. When I turn it up a bit so it calls for heat, reading across TT is 0.290v. When the flame kicks out, it reads 0.303v.
>
So that means the problem is not the thermostat or the wiring to it.
Do what @unclejohn said. Seems like a faulty aquastat.

JUGHNE

Don't jumper the gas valve itself......dead short!
Are we sure you have a standing pilot??
With the power switch off is the pilot still on?
You may have to lay on the floor to see it.

So if you have a standing pilot:
That rules out a faulty flame sensor (in the electronic sense, you don't have one).
It would also rule out a faulty thermocouple which is your flame sensor, if it keeps the pilot lite then it would be OK. Your pilot must be manually relit if it goes out.

Are there any other control devices that you have not posted a picture of?
How about a picture of the gas valve from the side that your meter leads are connected.

swm5126

Jumping B1 to the Z terminal and the flame kicks back on and stays on! So I guess that means it's the aquastat then?

HVACNUT

Yes, it's the aquastat. Get the same model or equivalent with the vent damper molex.

unclejohn

There are 4 numbers after the 8148e supplyhouse.com your best bet.