______________________________________________________________________ We bought a house 2 years ago with a HVAC Duomatic Olsen Ultramax II, Model HCS2 81AD, b.1987 and running on natural gas. It has 2 problems. Firstly a service contractor noted that it frequently shuts downs prematurely due to the ‘high temperature safety’. It will automatically restart when it cools down a little. He did not know how to correct this problem, except to replace unit or ignore the problem (we never even noticed it, room temperature always stays at thermostat set level.) The second, more scary problem is that sometimes it ‘kabooms’ on start-up and will not ignite, and retries several times with more ‘explosions’ until it lights. We have had 3 different contractors check it out. The first had the same furnace at his home, called it ‘dependable’ but did not have that problem and did not know how to rectify. He cleaned the ignitor and cleaned and adjusted burner flame ports. Second contractor had no idea either. The third, an employee of the local utility, Union Gas Ltd., replaced the pilot burner with a Honeywell Q345A 1305 as he thought that the previous pilot did not supply enough ignitions to light the gas. This new pilot sends ‘lots of lights per couple of seconds’, but periodic kabooms still persist? Please help. Waterloo Ontario is Canada’s technology center. Replies: wyrick “Re(1):’Exploding’ Duomatic Olsen” , posted Sun 8 Feb 09:12 ______________________________________________________________________ I have not worked on your brand of heater but have come across the same problems. Check orfice size for your altitude, restriction in your flue and combustion air. These may also shut your heater down on high limit. Wyrick vapourman “Re(1):’Exploding’ Duomatic Olsen” , posted Mon 26 Jan 22:27 ______________________________________________________________________ a friend had an “exploding noise” on intermittent ignition and it was dirty burners. xenos Webmaster “Re(1):’Exploding’ Duomatic Olsen” , posted Fri 23 Jan 20:53 ______________________________________________________________________ My first and only suggestion is to clock the meter and make sure its firing at the right input. It may be too high. Look Here http://www.hvacmechanic.com/howto.htm#where Xenos. The best way to escape a problem is to solve it.