Burnham holiday steam boiler starting problem (gas)

I have the above boiler which I had both gas hot water and heat.  I recently got installed a gas hot wate heater now use the boiler for just heat.  I had to relight the pilot because it was turn off back in march.  When i fired it up  I saw water actualy coming out near the discharge end of the piping where the prssure relief valv is.  I turned the heat off an the water level in the boiler was extremly high.  I went and let out alot of water which was red/brown in color.  I have to manually fill the boiler because it does not have an automatic switch.  Once the water was clearer I tried to fire it up again.  thermostat was on but he boiler would not fire up.  I then hit the low wate cutoff and it fired up.  it would only go for  a few minutes and then stop.  The water level in the sight glass is also bounching.   I tried to let more water out and add water at the same time.  Boiler still does not fire up.  I have to hit the low water cutoff every time.  HELP