Boiler controller replacement

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Old 01-01-14, 05:23 PM
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Boiler controller replacement

I picked up an older but unused condensing boiler on Kijiji a couple years ago to heat my workshop and have found the 'high' temperature control setting drifting since it was installed. I now have to set it to 180F to get about 145 - 150 from it, and the low and DHW differential settings haven't been predicatable since installed. Figuring it was just a dirty pot I set out with a can of DeOxit but noticed several capacitors and resistors on the back of the control board are completely burned. Guess that's why I got such a good deal on it

While somehow still working I know I'm working on borrowed time and need to replace the controller. The boiler is an NTI (NY Thermal) L75 with its integrated Sentry 2000 controller serving a single zone radiant floor. I left provisions for a future second zone on the 2nd floor but don't mind taking care of control for this through additional relays / logic if and when I ever get around to installing something upstairs. The boiler has provisions for DHW heating which I don't use, outdoor temp reset which I'd like to use but never hooked up due to the flakey operation of the controller, and a reset timer input which I don't use since I let the thermostat take care of unoccupied space temp reset and want to keep the boiler setpoint as low as possible for efficiency. I'm looking at replacing the controller with a Tekmar 260 and would appreciate feedback as to whether this is the best one for my application. Since pricing here is Canada isn't the best I'd also appreciate alternate controllers I should consider to compare prices.

Thanks
Rick
 

Last edited by Rick P.; 01-01-14 at 05:44 PM.
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Old 01-01-14, 06:52 PM
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Rick, is there anything more on that model number? All I see on their website is LX series. How old is the unit you have?
 
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Old 01-01-14, 08:11 PM
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I don't know exactly - it's a bit of an enigma and definately pre-dates the LX series. I'd guess 2005 or earlier. The model is called a Legacy L-75 and the installation manual I have for it (manual's actually for the L-150 and L-210 but the installaton is the same) was issued 2/18/2002. The service manual I have for it is dated 2/10/2009. There might be a date on the original box the accessories came in if it matters. The guy I bought it from bought it from someone else several years earlier and never got around to installing it. Apparently his wife heard something about people being able to put their car in the garage ...

I do know that there was nothing on the company's website about it and had to get the info I have directly from NTI. I was told when I bought it that the Sentry 2000 controller was non-standard and I'd have to MacGuyver something if I ever had problems with it. I've since found that the igniter control module and installed 120V gas valve were made of unobtanium specifically for NTI and have no cross-reference. That said neither of these is a big deal and I can work around both if I ever need to. Since the thing had never been fired (still had the plastic protective cover sheets on it), came with all the accessories, propane conversion kit and $200+ worth of stainless flex for $475 I don't mind if I have to spend a couple $hundred to bring it up to date.

Although it's not working properly now the mode of operation is pretty standard based on how it's supposed to work per the manual. The controller maintains the (reset) setpoint using the high, low (DHW) and differential settings based on operating mode. Since I'm not using it for DHW the burner should come on a High - DIFF and off at High + 10. The heat circulating pump logic has it coming on Low and off at Low - 10, but since I'm not using this for DHW it just runs when there's a call for heat since the boiler temp should always be above the low setpoint. Fyi, in my install I use a 3-way thermostatic control valve to maintain a 120F return water temp to the boiler. It was only after I noticed the boiler output dropping below 120F the controller issues became apparent.

I believe the Tekmar 260 works generally the same as above. Any thoughts?

Thanks
Rick
 
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Old 01-01-14, 08:17 PM
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I would like to see a wiring diagram if it's possible to scan and post a copy of it.

I believe the Tekmar 260 works generally the same as above.
Well... no... not really.

The 260 is only an outdoor reset controller. It's NOT a 'high limit' control.

You MIGHT be able to retrofit an AQUASTAT controller though...

Without knowing what's in the boiler it's hard to suggest a replacement.
 

Last edited by NJT; 01-01-14 at 08:33 PM.
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Old 01-01-14, 09:17 PM
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Not a full system schematic i'm afraid but it's all I have. It's the Sentry 2000 controller that needs to be replaced. The Sentry controller uses a thermister in the boiler tank to sense the boiler temperature. Sorry about the quality but the pdf I have exceeds the site's allowable file size.

Rick
 
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Old 01-02-14, 06:55 AM
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I actually was able to find a Sentry 2000 diagram for a different boiler last night.

I can barely read the diagram, but the lower control is the "Ignition Controller" and I presume that this must be working properly.

What I can't see though is the labels on the 2 wires on the ignition controller that come from the Sentry... It appears that there's an IN and OUT arrow on those two wires?

What do those labels say? (both ends of the wire, at the Sentry board end also)

I suspect that you could fairly easily replace the Sentry with something like the HydroStat 3250 aquastat control. It also uses a thermistor probe for sensing boiler temp. It has an interesting energy saving control scheme called 'thermal targeting' that bases it's calculation of boiler water temperature needed on the frequency and duration of thermostat calls... which makes a LOT of sense... rather than blindly looking at outdoor temps...

Basing a calculation on thermostat calls means that when the calls are few and far between the heat load is low, water temperature is lowered... when longer and closer together, the heat load is high... water temperature is raised.

This takes into account ANYthing that affects heat load... outdoor temp, WIND, OCCUPANCY, SOLAR GAIN, etc... Outdoor Reset alone is BLIND to the other factors.
 
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Old 01-02-14, 08:29 AM
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Excellent, thanks! There are directional arrows on the lines coming out of the Sentry feeding the WR igniton controller (which works fine) but there shouldn't be. These two feeds are labeled Line and Line common on the ignition controller and B1 / B2 on the Sentry - the Sentry simply powers up the ignition controller when the boiler needs to run.

I checked HydroStat's website and since the ignition controller is 120V it looks like their 3250 with thermal pre-purge enabled operates how the Sentry is supposed to, and then some. I forgot to mention it but pre-purge is important for me since the NTI is oversized for the current 800 SF load (and future 1600 sf too...) and its turndown ratio isn't very good. Sure beats the old 65% efficient direct vent DHW tank it replaced though! I really like the thermal targeting feature on the HydroStat.

Best regards
Rick
 
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Old 01-02-14, 08:50 AM
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since the ignition controller is 120V
You're absolutely certain of that... right?

I actually didn't mean to say 3250 model in my earlier post because I more or less expected that the ignition controller would be run on 24VAC... and this would require the 3100? model (not sure the model number of the 24VAC gas model)

Unless you are 100% certain that it is 120vac coming into the ignition module from the Sentry, it would be very wise to put the multimeter on there to verify.
 
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Old 01-02-14, 09:15 AM
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Yup - 120V, as is the gas valve. Seems everything on this boiler was OEM'd specifically for a single NTI product line and they're just not big enough to keep stock for what they sold. Whatever I have to replace on it over the next 15 years will require a bit of MacGuyvering...

Thanks
Rick
 
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