I have a Lennox complete heat sysem in my house and have had lots of trouble with it initially but has been very good for four years or so... Today I found the drain valve leaking so I drained the unit and replaced the valve and refilled the unit, when I tried to restart the unit I get "limit switch open" error message. When I first tried restarting I got sounds like grinding after four or five restart attemps these sounds stopped? Any thoughts?

Exactly what is the model number of your system. Is this a boiler?

Thank-you for your interest, it is a boiler and the model is hm 30. Since the post of my question I have had a professional look at the problem and he has determined that the circulating impeller is now a marble sized piece of plastic, he is going to replace that impeller to get the system running again and then we are going to look at our options and maybe do a re and re with a high eficient burner with an 80 gallon stainless tank. I know very little about these systems and on top of my previous question would like to know if this is a good option? The boiler currently heats my in floor heating and my domestic water. I am very disappointed with Lennox.

They have been discontinued quite some time back.
They were JUNK and made by Polaris.

Hand book

http://www.lennox.com/pdfs/manuals/Lennox%20HM30%20LP%20Manual.pdf

Install

http://www.hvac-direct.com/pdf_files/service/9821c.pdf

Dealer trouble

http://davenet.lennoxdavenet.net/Warranty/completeheat/Letter_2006_Tom_2006_10_01_Final.pdf

More stuff

https://www.cozyparts.com/Lennox-Parts/forum/post.asp?method=ReplyQuote&REPLY_ID=5641&TOPIC_ID=2367&FORUM_ID=2

NOTE

Do not put any more $$$ into that system than necessary. You WILL be replacing the complete system shortly anyway.

Many options available to replace this Lennox piece of junk. Get at least three bids to shake out all the loose ends. Many good brands of high efficiency 90%+ boiler units available to service your needs out there. The most important item is the knowledge of the installer for a good quality job.

Thank-you
I am going with a Canadian made IBC boiler with a twelve year warranty. Thanks again for your input.

If you have a fan coil or baseboard heat and the return water temp is at 130 degrees F or higher the IBC boiler might not go into the high efficiency mode. Be sure to have your contractor explain that because you will be spending $$$ for a condensing high eff boiler and it will not save you a dime over a standard boiler. Many folks are learning this the hard way. Good luck.

I have a 2700 sq ft home with inslab heat on two floors, the contractor seems to think this unit will save me money in the long run and he knows it is expensive... /