Mercury, no more..BN

Bill Nye_2

I can't buy mercury t-stats anymore. So I got the digital replacement. I put in a Weil McLain CGT gas boiler. It has a tankless coil and a 3 way divertor valve that gives domestic priority.

What does this have to do with thermostats? Well that is my question. It was late, the gas guy hung the meter just before 3pm, there were leaks [NOT ours] once I filled the system I had to protect from freezing.

So I didn't have time to play. It seemed like there was no 24 volt signal to TT until the boiler got to at least the low limit setting. I'm thinking this was something to do with priority? Once the boiler got above low limit I got a display on the t-stat. If the boiler went below low limit I lost t-stat display.

Any one had that? I "temporaried" and old mercry bulb t-stat for the week end. Everyone I talked to said use the resistor. I thought that was for taco zone valves. On the CGT I only have to wires that are labled t-stat, what would I jump with the resistor?

kevin coppinger_4

is it a power...

stealing t-stat? I use the battery powered ones...Lux PSD158...work well w/ everything....kpc

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Bill Nye_2

Kevin

It is the new honeywell T-87 replacement. Yes, power stealing , it needs 24v to operate. It only has two terminals, heating only.

lchmb

t-8400

I believe if your talking the T-8400 the resistor is only used on taco zone valves. As to an issue with the CG-T I wish I could help you. I did a CG-A the other day and had no problem what-so-ever. But have ,as of yet, not done the CG-T....

Glenn Harrison_2

Bill,

I can't specifically help you with the low limit situation, however might I suggest you try the new Honeywell Focus Pro series t-stats. You can change the t-stat in the set-up menu from a heat/cool to heat only, heat pump, heat only 3 wire, or even for a power to close zone valve. They are battery operated with option for a common wire. This is all we are using,and will most likely get rid of all the other mercury and non programmable units we stock (with the exception of 2 stage).

http://customer.honeywell.com/Honeywell/CatalogNavigator.aspx?Definition=Product&Catalog=Homes&Category=TH5110_26626&Product=TH5110D1022&ChannelID={2EB2F178-20ED-44E0-97FB-CCFB4218DD64}

Unknown

Hey Bill

The cheap, quick way out is to add a 24 vac relay. Take the hot from the existing transformer straight up to the thermostat, and back down to the 24v coil on the new relay (like a Honeywell R8222 or similar). Connect the other relay coil terminal back to the transformer's other terminal. Now the thermostat "sees" the set-up it needs.

Use a set of contacts on the new relay as the switch in the boiler circuit where the thermostat used to be connected.

Test it and you're done.

Noel

Jack_21

Braeburn

Non power stealing, and a bunch of very nice features. Fastest growing t-stat on the market. Do not sell to mass merchants.

BillW@honeywell

Hi, Bill!

The T8400 is power stealing, in all models. Glenn beat me to it, but now, I'm recommending that the FocusPro non-programmable or the VisionPro programmable be the replacements in areas where mercury stats are verboten. They're battery powered and compatible with just about anything. Those resistors you mentioned are for use with the TACO valves, also with the R8184G oil primary in some applications. Thanks to Noel & Glenn for your help!

Jaitch

Yes, Indeed!

How times have changed from the days when a T'stat was just a switch and didn't care if it EVER had power going to it. the microcomputer is changing all of that, for sure. Recommend the battery powered unit, or if you have the extra wires the seperate transformer seems to work OK.
As a footnote, if you have a soon-to-break thermostat wire, I have found it will carry the switch "on and off" signal OK, but will not be able to supply the "power stealing" t'stats. The stat will short cycle on and off repeatedly. Took me a while to figure that one out, so now we always run a resistance test on the t'stat wire BEFORE a changeout to a chronotherm or any other type of stealing 'stat.
Buy your AA and AAA's by the case! - Great source of future service calls -changed the batteries - system checks OK!

Robert O'Connor_9

Can you explain

the need for the resistor with an 8184 g with a hot air furnace? Thanks


Robert

ME

Glenn Harrison_2

Your welcome Bill

My pleasure. My bosses liked these so much that they ordered 100 of them so we could get our name/number printed on them, and now they go on every install.

Just out of curiosity, when is a two stage FocusPro coming out? It would be nice to get rid of all the "W" brand stat's we have.