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Joined on July 7, 2006

Last Post on October 24, 2013

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@ October 24, 2013 9:25 PM in Radiant Slabs tapped into Cast Iron System w/ Cast Iron Boiler

Thank you Bob,
I should have mentioned; there are thermostatic mixing valves in place, but the capillary sort. With the addition of the capillary bulb the valve actuates the temp. just fine. The amount of water actually returning to the boiler is matched to what the system draws... very little... due to the low temp. The circulators mostly just keep it all moving while it sips from the main supply. I don't think it could possibly shock the boiler.

I will just go ahead with the circulator zone control as there don't seem to be any objections.

Radiant Slabs tapped into Cast Iron System w/ Cast Iron Boiler

@ October 24, 2013 6:47 AM in Radiant Slabs tapped into Cast Iron System w/ Cast Iron Boiler

Looking at this system a friend is having a problem with. The original cast-iron HW system is still in place BUT two small bathroom radiant slabs have been tapped into the system.

They each have a thermostat and each thermostat runs to a relay which throws a circulator to the slab. That makes 3 circulators in total.

When the boiler is hot (the main system has been calling for heat) the tapped-in systems all work just fine. But on days when the main system is caught up, the slabs go cold as they are simply circulating unheated water through the boiler.

What would be the best(most efficient) approach to righting this wrong? My first impression would be to swap out the relays for a zone control (circ's) so each thermostat could call for heat, not just run a circulator.


@ November 10, 2012 1:39 AM in Wrong mixing valve? I don't see my error...

Many thanks to you guys. Especially you Gordon. I like details told straight.

This was a system I had built years ago. It sat in an unfinished home and was eventually all torn out by thieves. A friend of mine ended up buying the house recently. Since I laid the slabs, pex, and everything myself, I volunteered to make it whole again - pro bono.

So many years had gone by I forgot my design... in fact I forgot a whole lot. There never was anyone for me to learn from around here. Dan's books and this website were the only place I could really look to. Nobody I could learn from had a job and the rest had nothing to teach me.

I finished it today and had it working beautifully thanks to you guys. 'Best plumbers' where I live (a rough part of Philadelphia) did all the re-spuds on the cast iron rads, while they were there they took one look at it and said "The hell's this?'

Got a message from my friends as well... they will never go back... to cold feet.

Wrong mixing valve? I don't see my error...

@ November 7, 2012 8:50 PM in Wrong mixing valve? I don't see my error...

I hooked up this mixing station feeding a radiant slab from a traditional cast iron system. I can only get the loop to cycle and not feed from the supply (unless i throttle the ball valve in the center)
I have never used a mixing valve in this fashion... although the diagrams in the literature show A + B to AB or AB to A + B ... I ASSUMED I could flow A to B and have just some A to AB. Wow... let's just go to the pictures.

Can this V135A (Honeywell) work?
Many thanks,
Forever a grasshopper,

Tekmar 508 and Taco Zone Controls

@ October 13, 2012 1:51 PM in Tekmar 508 and Taco Zone Controls

Hi there,
I am running into issues with this set up. The story: I built this system many years ago, maybe 5... and it sat for some years in a house that was never finished. Thieves eventually broke in and cut out all of my copper work... leaving the electronic components and some pumps just dangling in the wind.

A friend of mine bought the house - and completed it - and as a favor I offered to rebuild the system. Unfortunately I do not remember what my design was... I just did my best to reimagine what I had originally planned and tried to fill in the blanks.

The issue I am hitting right away in with the Tekmar thermostats. When I connect them to the Zone control (with 120v circulators, not zone valves) They light up, but show no display. No numbers, no info, no error messages or codes. They also immediately cycle on the zones... each circulator slams on at once.

One relay clicks rapidly and the circulator fails to start. I am guessing that one is frozen from sitting out of use for so long (the system was drained but wet enough to rust I suppose). In this picture I have them disconnected to stop them from running constantly.

The thermostats I really have no guesses for... but this was my first time using this set up. I am not even gotten to the point of wiring the boiler, aquastat, etc. but just wanted to see that the thermostat wiring I had originally placed had not been damaged during the remodel.

These Tekmar units have a slab sensor as well... which is 2 wire. They control 2 isolated radiant slabs within the home.

Thank you so much... for your time


@ December 9, 2010 1:59 PM in Hitting a wall on old system

Since the relay is new - is there a method of testing it with a multimeter that would prove it has gone bad... I really don't want to order another one and wait for it. It's getting to be a very cold jobsite.


@ December 9, 2010 4:53 AM in Hitting a wall on old system

thanks ironman, I also thought it was the relay so this is a problem i've had after replacing it. I'll try switching to the 4 to the R

Hitting a wall on old system

@ December 8, 2010 9:23 PM in Hitting a wall on old system

I thought I'd have this old system up and running by replacing the relay control. I wired and rewired half a dozen times without any response from the system.

By jumping the Y and R terminals I can get the system to open the vent, start the gas, ignite via electric ignition. No pump action and certainly not safe, I just wanted to see if there was anything working at all.

That's the only way I can get ANY response out of this one. I'm just stumped.
Included is the Wiring Diagram off the front of the boiler and a diagram I drew while stumped that shows how I have it wired.

Thanks so much....

Mixing radiant into old cast iron system

@ January 6, 2010 4:56 PM in Mixing radiant into old cast iron system

Hi Everyone,
   Long time reader and occasional poster.

 I'd like to put in an entirely new system in an old house. I'd like to keep all the radiators and the excellently fitted old iron pipe while dropping in a new cast-iron boiler and 2 new thin-slab radiant zones.

I have done the heatloss calcs, layed out the pex, pressure tested, fitted slab sensors (tekmar) and laid the dry bed.

Now I'm selecting products to do the controls. I'm set on a traditional Weil-Mclain gold series boiler, but the rest is flexible.

I'd like to come up with a simple combination of controls to handle these 3 zones.
1 Large Cast Iron Radiant Zone
2 Barrier Pex Radiant Slabs

I was considering using set point thermostats in each of the slab zones, a programable thermostat in the main cast-iron zone.

I've built one copper and one steel system in the past, but have never used pex. I'm familiar with Taco and Tekmar controls.

My main concerns are coming up with a sytem with minimal components that can safely reduce the temperature of the cast-iron boiler for the PEX, protect the boiler from cold returns and ensure even supply of water when needed to all 3 zones. 

In the past I have used primary/secondary piping but with the PEX i'm not really sure how it's going to look.

Thanks for reading and for your time,
A budding radiant nut,
Tom Blair

@ April 8, 2008 7:40 PM in ???

the wall has appeared as blank to me for a week now. What happened? This is just a test post, as I'm guessing it won't show up.

@ March 21, 2008 7:38 PM in i did it

thanks! here are the before pictures. i know you guys like these. 188k WM with, unfortunately, completely busted steel pipes. it makes what i did look better.

forgot to add

@ March 21, 2008 7:13 PM in i did it

this is the style of radiator i have, and i reconditioned about 20 of them, pressure tested, sandblasted, repainted and changed the spuds. next time i'll put a bag over them to keep the drywall dust off. edit: in the bathrooms they are blue, bedrooms black and in kitchens gold or beige.

@ March 21, 2008 7:00 PM in i did it

here are a few pictures from a week ago, before i connected each zone, cleaned up and affixed the wires in place and did a few other small things. i'll get a picture of it in its final form for you. its much neater now. the blue radiator is in a small bathroom. the whole system is piped in copper and in reverse return.

it is accomplished...

@ March 20, 2008 5:57 PM in i did it

i'm an everyday lurker, sometimes poster here. i read a few of dan's books found this sight and through the use of both, i learned to build a hydronic system from scratch. today was the realization of that goal. i fired the WMcga3, spark ign. and got my primary loop heated up in just a minute and a half. i flipped on the electronic control side of my system and the heat was transported, quickly and quiet as a lamb to the 4 zones i piped in my building. the american made thermostatic valve worked exactly as it should, and with a little fine tuning i had even heat in every radiator simultaneously. it was my greatest moment of triumph within a much larger project. i'm not one to ever be proud of myself, but i can't help it now. i want to thank you all for sharing your wisdom with me. i will continue to better myself and my understanding of hydronic heat and spread the gospel of steam and water. Tom

@ March 14, 2008 1:29 AM in new type of base board

sounds like the classic oil-filled electric that mimics the look of a traditional cast-iron sectional.

what all this?

@ February 27, 2008 10:10 PM in boiler install pics - oil, hydronic basebd.

does that bx have a blue stripe?


@ February 19, 2008 2:24 AM in question for engineers

thanks. that was the bit of advice i was looking for. that really is the distinction... yes. i want both worlds. i will try to find a way. thank you


@ February 16, 2008 8:21 PM in question for engineers

nevermind i'll find help somewhere else.

@ February 14, 2008 6:21 PM in question for engineers

thanks guys. i'm happy to give more details. i'm 26, i have a degree (BA) in art history and architectural studies. my specialty was baroque architecture. i know... i know. i'm at square 1. i was a teacher out of college, since then i've been working for myself- restoring victorian houses in the northeast for the last few years. i'm happy to go back and take undergrad classes to get into the right program. i have a strong desire to learn and nowhere else to turn to. while teaching myself what i could get my hands on - i read 3 of dan holohan's books... that's how i ended up here. i took the GRE on my own time and did pretty well. the verbal was ok, 600-something i dont remember, but i was shocked to get a 790 on the quantitative section, 5 on the writing. i never took a math course in college. i know my brain is wired to be an engineer. i was always pushed by my family to be an artist or architect. i'm good at that but its not me. i love big machinery, physics, energy, big projects and new ideas.


@ February 14, 2008 1:51 AM in question for engineers

heating and cooling with water fascinate me. i don't know why. i love the mechanics of energy transfer. i'd like to work with geothermal sources. i prefer a creative environment. i like to invent. what kind of graduate program would you recommend for someone like me?

@ February 12, 2008 6:42 PM in running out of ideas..

sounds like the pump - if not a physical blockage... just my opinion

@ February 11, 2008 6:26 PM in I believe it is spelled 'faux pa'...(off topic)

yea... the faux pas, the false step. but timco if you feel the regret you shouldn't worry on top of that. the regret you feel demonstrates that you are sensitive person. lately i've found myself whistling 'everybody plays the fool' and just thinking about how true that is. we all play the fool some time or another.
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