I just figured out last night that my Hunter HDV30 gas fireplace also was not firing up because of a bad mercury safety switch.
What I did was hotwired the two connectors in the porcelain base together and the main burners fired right up nicely when I flipped the switch. I know this is bypassing the safety, but I'm wondering how safe it is to just continue doing this in light of all the difficulties in finding a new safety switch. I'm perfectly happy to shut the pilot off after every use and start it up manually before using my fireplace. I'm just wondering what the risks really are.
I would still like to get this fixed properly of course... It seems first that Hunter has vanished as their phone number is now a tanning salon. I've looked at Repco's catalog and I don't see an obvious replacement to the part I need as its documented in my manual. In there it is called a "Mecury Vapor Switch" with a part number of 916243.
The function of this part seems pretty basic - surely there's something else that could be used in its place?
Other than for testing you should never bypass part of the safety system. The mercury vapour was was designed to shut gas off quickly in the event of a pilot failure. Napoleon in Canada has some valve and pilot assembly changeouts for some of their models. Hunter and CFM can also be changed out with a vavle and pilot assembly. If you want to contact me with your model numbers I can tell you if parts can be found.
You say "shut gas off quickly in the event of a pilot failure" .. do you mean gas to the main burner or gas to the pilot? If it is gas to the main burner, what I don't understand is that if the main burner is burning, how is it even possible for the pilot to go out?
If its the pilot, then why does the gas to my pilot not shut off now with a broken mercury vapor switch?
My fireplace is a Hunter HDV30-e-3
In my manual, it lists the part as this:
part number: 916243
description: Mercury Vapor Switch
I also find it very curious that there is no replacement part for this that contains no mercury... seems like a pretty simple mechanism to me, but I'm no expert.
It interrupts the gas the millivolt flow to the operater coil that opens the main gas flow through the burner. It senses that the pilot is active so that there can be little build up of gas in the combustion chamber with no flame present to ignite the gas. The standards that direct vent fireplaces fall under require that the gas flow if the pilot goes out shuts down very quickly (I believe 30 seconds is the maximum). Thermopile systems can take 3 times as long to shut down.
I'm sure it's just a question of economics to build a direct replacement for the mercury switch and have it tested and approved would cost a lot of money and I don't think most would pay the part for the price. Most fireplaces that used the Mercury Flame sensor can be fixed by replacing the pilot assembly and gas control with approved components.
Makes no sense? You said your burner runs with that switch failed. Did someone play mechanic and provide an engineered bypass. Mercury is not used anymore in these products, just like mercury thermostats are gone, mercoid switches etc are done. That's why everyone is telling you that you probably won't find one unless someone has some old stock. But back to your issue, if I understood you correctly you now have no pilot safety but the burner operates? I would shut it down immediately and call an expert to provide a new ignition control for this unit. Burner on with this control broken IS NOT NORMAL and UNSAFE. Hopefully I misunderstood your post.