OLD Boiler Bi-metal Switch

pclam

I have an old - circa 1916 - coal-burning boiler that was converted to gas probably in the 40’s. It has a Roberts-Gordon burner and a Honeywell 155A valve. It has a standing pilot with a bi-metal safety switch. It been chugging along for the 33 years we’ve lived here.

Here’s the problem: when the burner is turned ON, it’s stays on for about 30 seconds then the valve closes per normal operation. I’ve done a little troubleshooting and have discovered the following:

1). When pilot is lit, the switch closes as is required by the valve.
2). As long as the pilot is lit, the switch remains closed and provides continuity to the valve.
3). When the burner is fired however - with a jumper to replace the switch contact closure - the switch stays closed for only about 30 seconds at which time continuity is lost and the the valve closes.

Clearly, the switch is not functioning correctly, but why would it close and then open when the burner fires up?

Also, is a replacement for this type of pilot assembly available?

I’d greatly appreciate any thoughts or advice you might have

Images attached

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Big Ed_4

If you want to keep the old pancake boiler I would recommend replacing the burner and controls …. With the lack and age of the safety's on your burner , it increases the chance of a hazard ..… Quit while you are ahead as they say …

delcrossv

Agree with the above. Replace them both. The present power burner may keep running or not.

I noticed the gearing onthe gas valve is pretty worn. It's time has come.

If the present burner were atmospheric (no blower) you'd just need to swap the gas valve.

You should keep the old one. It's a historical artifact.

EBEBRATT-Ed

It's time for some new equipment. Roberts -Gordon is long gone.

It sounds like the pilot sensor is dropping out when the main flame come on. Could be a gas pressure issue.

unlikely that you can obtain any parts for that burner

I would suggest replacement with a modern gas burner but with the age of the boiler putting that kind of money into a boiler that old may not be $$$well spent.

That boiler is probably around 100 years old.

delcrossv

Dunno, those old boilers don't seem to have a limited lifespan.

mattmia2

like @EBEBRATT-Ed said, it is probably not the switch, it is the pilot flame either moving off of the sensor from the draft of the burner moving the flame or shrinking because of a gas supply or regulator problem and causing the sensor to cool and open the switch

EdTheHeaterMan

A photo from farther back would show the entire gas train.   Then we can say what parts can be eliminated and what other parts can be used to replace them.  The old gas train from the hand actuated manual valve to the flame may include a pressure regulator, the electric gas valve and some sort of pilot safety switch, and perhaps some other parts.  You can remove much of that stuff and install a modern redundant gas valve that has the regulator and pilot safety built in.  You may even upgrade to a spark to pilot electronic ignition for that old burner.   As long as the housing of that burner can still hold the main burner and pilot burner in the proper position, there is no reason that the old burner needs to be abandoned. You just need a place to hold the thermocouple or electronic ignition sparker and flame sensor.

EdTheHeaterMan

It might look a little like this

pclam

Thank you all, for your helpful comments and creative suggestions (love that rendering of the potential upgrade!).
Would it make sense to start by having the gas pressure checked? And would any heating guy be able to do it, or do I need someone with experience with old beasts like mine?

mattmia2

you need to find someone that understands combustion and old gas controls

pclam

Anyone know of anybody in the Boston area that would be qualified?

delcrossv

https://www.heatinghelp.com/find-a-contractor/state/MA/

EdTheHeaterMan

The old boiler and gas conversion burner may be a nice look for an old home. There is another thing to consider though. What does it cost to operate. In many cases a new modern boiler will cut your energy cost in half. So consider how much your gas bill is in February. If it is under $150.00 then it may not be cost effective to replace. But if it is over $300.00 then you may be paying for a new boiler anyway. That payment is actually going to that gas company and you are letting 1/2 of that bill go up your chimney as wasted fuel.

Here is an easy way to figure out what your heating costs are (approximately) if you have more than just heating appliances.

• Add up all the gas bills for the entire year
• Look at the lowest gas bill
• Multiply that by 12 for the whole year
• Subtract that from the total for the year
• What's left is your heating costs.

With that information in hand, multiply that estimated annual gas used for heating by 0.4 to see what you might save with a new modern boiler. Multiply that by 10 to see what the 10 year savings is, and compare that the price of a new boiler. If it is lower than the savings estimate, the you are paying the gas company for a new boiler anyway, and you still have the old wasteful beast in the basement.

Something to think about.

Sometimes a new boiler is not going to save you enough to pay for itself. Every home is different. and if you are paying $200.00 or $500.00 or more to make that relic waste more fuel, Then ifit makes sense to use that $$$ as a down payment on something better.

Jamie Hall

Someone in the Boston area? @New England SteamWorks . But chances are they're very busy — and probably will say to replace the thing.

Any good tech. who knows their way around a manometer can check the gas pressure, though.

Now. Having said that, you should remember that a bimetal switch has only three modes of failure. Apparently in your case two of those modes aren't present: the bimetal is intact and the contacts close. What isn't happening is that the bimetal isn't staying hot enough. Pilot flame size or location…

pclam

Update for those who are interested:

I called a local company who sent an older guy who seemed to know his way around these old systems. He did not, however, have any testing equipment. When I asked him to measure the draft he said, “I did - I just stuck my hand in”.

This was disappointing, since based on comments in this thread, I thought the draft might be part of the problem. So I experimented a bit with draft regulation.

First, I increased the opening of the inlet panel next to the burner (a little sliding panel could be pushed back). As a result, the boiler ran for 30 minutes instead of 30 seconds.

Second, I tried running it with the main door to he boiler half open. This gave a running time of almost an hour before the system cycled off. I’m guessing that what I did decreased the turbulence near the safety switch flame.

Does that make sense? And is there another flu or draft adjustment I should try? I’m not crazy about running the thing with the door open!

P. S. I’m just looking for a temporary fix to provide heat until we can either do the updates noted above or get the whole thing replaced.

An image of the burner with open panel is attached.

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Jamie Hall

I really wouldn't be happy running with that door open — but manually adjusting the draught with the sliding door as a temporary — very temporary — measure is tolerable.

Having said that, don't be too hard on that old-timer. He's probably done a few thousand of these, and has a pretty good feel. Which is not to say that you shouldn't get someone there as soon as possible to check everything with mor up to date equipment.