Advice needed on fixing noise in a radiant in-floor system

[FinsToTheLeft]

I'm looking for advice on fixing a system which is driving me CRAZY with noise.

A little background:

I purchase my house - a 100 year old, three story, fully renovated - back in the summer of 2007, so this is my second heating season.

We have in-floor radiant heat supplied by a Slant Fin boiler (for heating only - no hot water). Each floor is zoned seperately with a manifold that divides the floor into 2-4 loops. As far as we can tell, the pipes are stapled up in the joist spaces beneath mostly hardwood floors. This system was installed the year before we purchased the house. I do not know who installed the system, nor do I have the engineering drawings.

We regularly hear a noise coming from the floors when the heat kicks in that sounds like a popcord popper. I think that this is the PEX moving as it expands rather than trapped air. There is a bleeder on the boiler (although no air scoop) and auto-vents on each floor at the manifold.

I had someone in this week who believes that the system was plumbed improperly. The system looks like this:



The technician explained that essentially the pumps and the mixing valves are reversed which leads to 160 degree water is being delivered to the loops causing the rapid expansion. The boiler is also running on an approximate 3 minute cycle and the only temperature control is supplied by the limit switch.

He wants to remove the current setup, put the mixing valves between the boiler and the return and then put the pump above that. In addition he advises adding a temperature control that adjusts the boiler temp based on the outside water.

Sorry for the long winded message, but I just want to make sure I am heading down the right path before I spend a lot of money and hopefully let me sleep through the night!

[FinsToTheLeft]

Does anyone have any advice on this? I just received an estimate of $2600 for the re-piping and supply and install of an outside temp reset control.

[ZL700]

Tough to see all with the flex duct in the way and the angle of pic but it does appear to be piped really bad.

The circs should be drawing from the mixed water temp outlet (opposite dial) and it looks like they were tied in with hot water inlet and the supply to the floor?

Those ball valves were then cracked open to get some flow to floor which would be the uncut boiler temp. If the ball valves were closed, it looks like the installer attempted to push through the hot inlet which won't work and thus can't draw any cold into the mix valve.

YES YOU ARE IN NEED OF REPIPING

After that, an outdoor reset may not work so well for you because of the thermostatic mix valves. If the outdoor controller operates below setpoints of mix valves, they will search for hot water and thus probably not have enough flow to add heat to floor loops.

Question is, do you need 2-3 different supply floor temps to satisfy the zones, or are they all set the same. If the same then an outdoor reset control with max boiler temp could be used. If different supply temps are needed, then it would be best to just set boiler max temp to highest floor water temp required and leave it alone.