Need Help Troubleshooting Gas Boiler – Burners Not Igniting Consistently

Eddieblade21 · November 10

Hello all,

I came here hoping some of the professionals might be able to help me figure out why my gas boiler won’t fire up consistently.

When I raise the thermostat above room temperature, I hear the relay click at the boiler, so it’s definitely getting the call for heat — but the burners don’t ignite.

Here’s what I’ve done so far:

If I cycle the boiler’s power switch off and back on, the burners ignite and the boiler runs fine until i lower the thermostat below room temperature (not sure if that was coincidence).
After lowering the thermostat to normal and trying again later, the burners fail to ignite again.
I lightly tapped on the White Rodgers 2509-256 solenoid gas valve, and the burners ignited immediately (not sure if that was coincidence).
I drained the expansion tank and bled all the radiators.
Pressure on the gauge is 12 PSI cold and about 20 PSI when running.
Water temperature reaches around 145°F when running.

It seems like either the gas valve or something in the control circuit isn’t engaging every time. Any insight, tests, or next steps you’d recommend would be appreciated.

I've included several pictures of what is on the boiler, any receommemdation would be appreciated. I plan on cleaning up all the wiring cause it bothers me. Also as far as maintenance what are the recommendation? any susggestions of upgrading these old parts. Please note this unit has been workign flawlessly for 20 years.

Please feel free to ask all the questions, I have tried to give as much informations as i can and sorry if i left anything out.I cannot thank eveyone enough in advance.

White Rodegers 2509-256 Gas Solenoid.JPG

EdTheHeaterMan · November 10

You have an old system. Over 50 years old. I wonder if there is a wiring diagram attached to any of the panels that are removable? The dual Aquastat marked Circulator / High Limit indicates that at one time there may have been a tankless coil for DHW. Where do you currently get your hot water? a separate tank perhaps.

The three identical boxes with "Lobster Tags" (center one indicating Attic) would tell me that you have 3 circulators and three thermostats

Tapping on the heater making the burner start indicates you have a relay that is being powered but is not getting enough power to pull in the solenoid or relay, but with a little percussion adjustment (like the Fonz at the juke box) will get the job done. This could be indicative of a failing transformer, dirty electrical contacts or a failing coil on a solenoid gas valve or relay clapper.

Can you post photos from farther back so I can see how this is put together.

EDIT: the 24v. 3 VA transformer indicates that at one time there may have been an old Chronotherm clock thermostat like the TM850 that required a separate 24v. power supply.

Eddieblade21 · November 10

Correct

3 Thermostat one on each floor. The water is supplied directly from the main feeding the house provided by the city/town. There is not seperate tank feeding the boiler.

I definetly can take a better picture of the entire system when i arrive home

EdTheHeaterMan · November 10

@Eddieblade21 stated: "It seems like either the gas valve or something in the control circuit isn’t engaging every time. Any insight, tests, or next steps you’d recommend would be appreciated."

You are correct, however there are so many place where that can happen when you have a high limit that ols and three circulator relays.

@Eddieblade21 stated: "There is not seperate tank feeding the boiler."

I believe you misunderstood my query about a separate tank…. When the people in that building take a shower, where does the hot water dome from".

A tankess coil inside the gas heater?
A tankless water that hangs on the wall?
A gas water heater that includes a tank and a gas burner with a vent pipe that goes into a chimney?
An electric water heater that is made of a tnk and some electrical elements inside the tank that heat the water?
A fire place with a boiling water kettle that swings out away from the flame so you can draw some hot water in a bucket and carry it up the the shower and pour it on the showering person?
OTHER

I ask because of the control marked circulator. There would be no need for a circulator limit control with a standard boiler that does not have a tankless coil for Domestic Hot Water (DHW) when equipped with switching relays for each circulator pump.

HVACNUT · November 11

Stop on the way home and pick up an electrical meter if you don't already have.

mattmia2 · November 11

have to test it with a meter. that boiler was probably 50 years old when @EdTheHeaterMan was mid career, those gas controls are from the 50's or maybe 60's.

You have to trace it with a meter and figure out what is not closing or doesn't have voltage or isn't opening when it should be. Start with the gas valve when it is calling for heat and not firing and see if it has 24vac there. If there is no voltage than it is a problem with one of the controls. If it does have voltage then the valve or maybe the regulator is sticking. That is kind of a more involved and expensive fix if it is the gas controls, that is either a retrofit to a modern valve or a new boiler.

If it is the other controls, those are relatively easy to replace.

EBEBRATT-Ed · November 11

"

mid career? maybe 1992 ish-50=1952? I think that boiler is probably around that old. Maybe a few years later.

With that solenoid valve would that have an old pilot safety switch? I would think so.

Eddieblade21 · November 12

Hi all,

Thank you so much for all the help so far — especially @EdTheHeaterMan for the detailed explanations .

To clarify a few things: yes, this system originally had the old Chronotherm clock thermostat, and there’s a separate gas-fired water heater for the domestic hot water (not tied to the boiler). You were also correct — the system has three separate zones with three individual circulating pumps.

I began testing all the circuits for proper voltage and found what I believe was the main issue:
The lower transformer was shorted on the 110V feed side, which in turn appears to have burned out the Aquastat and transformer.

As I dug deeper, I noticed the wiring wasn’t really up to par with the components installed. For example, one zone’s thermostat (T-T) was connected to the old external 24V transformer (the “silver one” that failed).

To clean things up, I decided to rewire everything from scratch, eliminating the old cloth wiring

Rewired all three RA832A relays correctly,
Wired each Nest thermostat directly to its relay’s T-T terminals, and
Confirmed the boiler switch hot and neutral were spliced to feed all three relays and the Aquastat.

I also ordered a new Aquastat L4081B to replace the fried L4010B.

Questions / Clarifications

Should the hot wire from the boiler switch feed the Aquastat first and then jump from the Aquastat to terminal 1 on each RA832A (with neutrals tied to terminal 2)?
The silver transformer—I’m assuming it was originally used for the old Chronotherm clock thermostat, since each RA832A already provides its own 24V. Can I safely remove it now?
The X-X terminals on each RA832A:
- Should these be wired in series or in parallel?
- And do they connect to the T-T terminals on the Aquastat?

From what I’ve gathered, the X-X terminals act as isolated dry contacts that close when a zone calls for heat. My assumption is that wiring them in parallel would allow any zone to signal the Aquastat to fire the boiler (vs. series, which would require all zones to call at once).

Does that sound correct?

Thanks again to everyone who’s been helping me work through this. I’m almost there — just want to make sure the final wiring is done properly and safely.

mattmia2 · November 12

the x-x would be in parallel and go to the relay that fires the boiler or to the safety chain and gas valve depending on how the boiler is wired.

the aquastat needs to break the control signal to the gas valve. the simplest way would for it to be in series with the gas valve though it could be in series with a relay controlling the gas valve if the boiler is set up that way. If the aquastat is in series with the gas valve directly there are less components to fail and result in the boiler not shutting down when it should.

is there only a circulator for each zone or is there a 4th boiler circulator?

mattmia2 · November 12

If it has a pilot safety switch it is critical that is also in the safety chain to the burner.

Eddieblade21 · November 14

Hi All

@mattmia2 sorry for the delay in responding the Gas boiler has one circulator per zone no addtional circulator. After a long issue re-wiring the entire boiler, replacing my ancient aquastat my system is fixed, but have one more issue. Pleae note this boiler is way over 50 years old. I need to replace the what i assume is some sort of flame sensor, it has a Red and White wire in a protective flex metal shield and mounted on the pilot assembly. I need to change it but dont know where to start or what is to understand the function of it. Please help

EBEBRATT-Ed · November 14

I am guessing you have a pilot safety switch usually made by BASO although I don't see it in the picture. Can you show us what the metal flex cable goes to? Baso is still in business if that is what you have.

Also are your Nests wired with a two wire cable or three wire? Do you have a wire to the C terminal on the Nest?

Eddieblade21 · November 14

Hi

In the picture it is the rectangular piece that sits between the burners rhe pilot flame sits right in front of it

It was connected in series red wire to one leg of the transformer 24v and the white wire was connected to one leg on the gas solenoid valve

I dont know how to test it to make sure it is bad or good

I have it disconnected and checked the continuity of the sensor and shows open

My three nest thermostats are 2nd generation which are only connected cia 2 wires W1 and Rh

mattmia2 · November 14

I believe that is a thermostatic pilot safety switch. long ago obsolete. not sure of the safety of it but you'd have to replace it with a thermocouple and baso switch if you replace it.

Eddieblade21 · November 14

HI do you think this will work, as my searches say it was a vintage thermopile.

Please see link from Baso

T36A1 Series Universal Thermopile Replacement Kit

Please advice or any recommendation you might have

mattmia2 · November 14

is there a transformer? does the valve say 24vac or something like 750 mv? does that device have continuity with the pilot out? what if you light the pilot and wait a minute?

looking at the picture of the valve i think it says 25v?

if so that is not a thermopile, it is a thermostatic switch

Eddieblade21 · November 14

Yes, there is a 27.4V transformer, it reads 27.4V coming out of the transformer.
i measured the unit’s continuity while the pilot was on and it read OL.

mattmia2 · November 14

The replacement is this(wait for a second opinion from someone that knows old gas controls better but i'm pretty sure that is just a switch heated by the pilot burner):

https://www.supplyhouse.com/Baso-Gas-Products-L62AA-5C-SPST-Manual-Reset-Pilot-Switch-w-Non-100-Shutoff

and this:

https://www.supplyhouse.com/Baso-Gas-Products-K15FA-36H-36-Thermocouple

might need a bracket to mount it in the pilot burner or to replace the pilot burner.

you could also replace the whole gas train with a combination valve or intermittent pilot conversion kit but you would need a gas tech to set up the new valve properly.

was it not firing before?

try tapping or wiggling the switch and see if it has continuity sometimes