Advice on heating system

Hi everyone,
I have two questions on my domestic hot water / in-floor heating system. I've attached a hand-drawn schematic for your reference. We just moved into this house four weeks ago and since it's summertime we haven't really put the heating system through its paces. The biggest load we've put on it is an extended shower and there's plenty of heat for that.

1) Both water heaters are high efficiency models less than four years old and both are equipped with White Rodgers Intelli-Vent controllers. Both are set to the same setting which, according to the manual, should keep the water temperature around 135F. Heater #1 is a 40 US gallon model and #2 is a 50 US gallon model. I've noticed that #1 fires a lot during the day but #2 fires rarely, if at all. Does this setup seem right? I was wondering if #1 should be set to a lower temperature in order to share the heating load across the two heaters.

2) I've also noticed that heater #1 usually takes several attempts to light. The fan starts, the ignitor gets hot, the gas comes on and lights and a couple seconds later the flame goes out - I've watched this happen through the sight glass. On occasion I've received error messages on the controller that it temporarily locked itself out for too many unsuccessful lighting attempts. I was wondering if the heat sensor (thermocouple) got bent out of position but it looks like it's in the right place to me (see attached photo). I'm wondering if the thermocouple is bad. Any ideas how to test that? Any other ideas what could be the problem?

Thanks for your help!

Grant

Water heater #1 is the work horse of the two. Hot water flows from #1 into #2 then to the fixtures. While hot water is flowing into #2, cold water is refilling #1 causing it to fire/run more often than #2. The flame sensor seem to have a bit of buildup, clean the flame sensor with plumbers sandcloth or very very very fine sand paper. Cleaning the flame sensor might take care of the water heater not firing properly/working proper. With a dirty flame sensor the flame can't be sense and the heater will shut down and retry to fire. Be careful not to touch the ignitor, the oil from your hand will shorten the life of it. Just a side note, If your sprinkler system is on soft water you should have it move to hard water.

This system is not setup very efficiently. First of all the piggy back method is a waist of space. Just like stated above #2 will rarely operate. Infant it will not do much until #1 fails. If you're pumping 135deg water into #2 it is not going to need to heat. It's acting as a storage tank which is obsolete and also acting as a backup heat source. What is sad is that #2, although is not burning is under pressure and you are just waisting the life span of the tank. Thermal couple is probably why won't stay lit but it could be something else such as incorrect venting. If these tanks are not vented right, you might have a back draft issue blowing the pilot out. Many other things we could go over but this is where to start.

Thanks for the advice. I gently sanded the thermocouple as IFIXH2O suggested and the heater fired and stayed lit first try. We'll see if it keeps it up now. I just installed the water softener last weekend and as I was drawing the schematic, I came to the same realization about the sprinkler system. It's just a rough-in, so unless I get really ambitious I'm going to leave it for now.

AQualityPlumber - can you explain to me what you mean where you wrote that although tank #2 is not burning it's life span is being wasted? I'm not sure I understand why that is. What are your suggestions on the control temperature settings? Looking around the house, I get the feeling that the previous owner wasn't much of a handyman so it's conceivable to me that at one point he turned both down to vacation and then couldn't remember the settings when he got home and just turned them both up to the same setting. Do you (or anyone else) have a recommendation to the proper settings for the temperature controllers?

I would not change the settings until you see how it performs during the heating season. That is the reason for the 2nd tank. You can be sure the 2nd tank will fire during the heating season. There is no way one tank could supply you with domestic hot water and heating. By making some changes to the piping you could take the 2nd tank out of service during the summer months.

Tanks continue to corrode as long as there is water inside the tank. Although #2 is not doing much, it still has hot water flowing through it. That is what I mean by you are waisting the lifespan of the tank. It will likely go bad after 6-10years of use and like I said previously even though it isn't firing often it still has pressurized hot water flowing through it at all times. Therfore it is in use at all times.

unsure of the code where you are but where I am you cannot use a hot water tank for space heating applications unless it is designed specifically for this application ( combi core or similar ) also as others have said what you have there is a SERIES system and what would be more efficiant would be a PARALEL installation ( in a paralel installation all pipe lengths between the 2 heaters are identical and the supply comes from the mid point, thus splitting the load over the 2 heaters instead of one doing the primary work. also with a paralel install both tanks lifespan should be similar. Depending on where you live and how cold it gets there your tanks may die at a young age.