I have an Ultra 97 gas fired heater made by Magic Chef. I assume its about 15-18 years old.

When the heater kicks on, the only thing that happens is that the blower starts running but the ignitor does not ignite. There are 2 flat cylinder type switches when you open up the door. If you tap on either one of them , then you start to get a clicking sound and the furnace fires up. They are made by Tri Delta Industries which I found out has gone out of business.

I assume these are high and low pressure switches but Im not 100 % sure. Do you think these need to be replaced or do I have a problem somewhere else ?

The previous owner told me I needed to add a 1/4 cup of water into a tube that is on the side of the furnace. Can anyone explain what that is all about ?

I tried replacing the ignition module Robertshaw 780-715U and it worked for a couple days and then stopped again. I have to tap on the limit switches in order to get it to fire up or start clicking and then it ignites and works for awhile, reaches desired temp and shuts off. It seems that when it is off for a few hours and the temp drops, and the thermostat calls for heat , is when I have to go downstairs and tap it and it works.

I tried testing bthe switches to the pressure switches to see if they were loose and the flame would drop out, but it did not, furnace remained lit

You should probably call for On Site service. You have to many items happening on that old furnace. It probably has not had a cleaning and service for years. At that time the service person will probably have switches that he can replace those with if they are what I am thinking they are. Make sure they test the heat exchanger since the old Magic Chef/Armstrong units had some problems with that. I am telling you this for your safety.