Boiler Mate and Dunkirk Boiler water scalding

[TequilaMB]

We have a Dunkirk Boiler Model XE4, and an Amtrol Boiler Mate Watermaker model WH-7L, approximately 30 years old.

We recently began having problems with the Amtrol unit over-heating the water to the point of being scalding, no matter where the temperature gauge is set. We replaced the thermostat on this unit - twice. Both times, the unit "behaved" for a short period (like, a week or so) and then began over-heating the water again. The only solution we've found is to shut down the Dunkirk boiler altogether, and let the water cool down. When fired back up, sometimes the water stays at a normal "hot" temperature for a day, or a week, and then goes into scalding mode again. Obviously, shutting down the boiler is not going to be a solution come winter. Any ideas on what could be causing the issue? We've had our plumber in, who is a Dunkirk Boiler man, but evidently not an Amtrol man, because he said this is "not his area of expertise". He's also said that the boiler "won't blow up". Understandably, we're a bit skeptical of his expertise at this point!

 

[Dana]

The boiler isn't going to blow up as long as it's high-limit aquastat is working (what is it set to?)- the problem is totally 100% within the controls for the indirect, not the boiler. But it would be good to know why the controls for the WH-7L are crapping out, or working only intermittently. It's possible that after 30 years of service the thing is sufficiently limed-up on the inside that there is no longer sufficient thermal conductivity to the sensor (?). Whatever it is, after 30 years it doesn't really owe you anything- a typical lifecycle is more like 20-25 years before it either leaks or limes up.

The sure-fire solution to the scalding water issue would be to install a thermostatic mixing valve at the output of the indirect, to be able to independently set the temperature of the water entering the hot water distribution plumbing, independently of the storage temperature. Current codes already call for either a tempering valve or thermostatic mixing valve between the water heater and distribution plumbing to any sinks or bathing (except for laundry or direct to a dishwasher), so even if/when you get around to replacing the water heater it won't be money wasted to have already installed a thermostatic mixing valve.

The XE4 is getting a bit long in the tooth too, and is almost certainly 2x+ oversized for the design space heating load for the house. If it's continuing to work OK there is no burning need to replace it, but it's time to think about what the replacement might be. The last thing you want to do (from both an efficiency and comfort point of view) is to replace one ~100KBTU/hr boiler with something of equivalent output. A typical 2000' 2x4 framed house with storm windows over antique glass and no foundation insulation comes in with a heat requirement of about 40 KBTU/hr @ 0F or ~50K @ -20F. The XE4 delivers about 95K. ASHRAE recommends an oversize factor of 1.4x the heat load at the 99% outside design temperature for the location, which is enough to cover the actual heat load even during Polar Vortex disturbance cold snaps, but not so oversized that it suffers from low duty cycle/high standby loss, or glacially slow recovery from overnight setbacks.

To get a handle on your actual heat load, using wintertime-only gas bills, run a fuel-use based load calculation to find the right ballpark. With more information (such as thermostat settings, radiation sizing, outside design temperature) it's possible to come up with reasonable suggestions of what might deliver better comfort & lower cost (both up front, and ongoing) when the time comes.

 

[Sponsor]

 

[TequilaMB]

Thanks for all that information! I will pass it along to the hubs, and we will need to digest it.

 

[Sylvan]

About installing a tempering valve even Holby which I consider the Rolls Royce of tempering valves is not considered anti scald protection as it is slow acting unlike a temperature or pressure type of anti scald device

I used to think by installing a temperting (mixing valve) the occupants were protected but after working as an expert witness for over 37 years I realized people no longer take personal responsibility and with the influx of people who are not accustomed to having hot water there is a lot more scalding then ever before

NYC had no maximum temperature hot water temperature and then after the lawsuits started coming in the courts were overwhelmed


So they made revisions of the 1968 plumbing code setting the temperature to a max of 140 deg F but did require showers ( not existing) to have the temperature set for a max of 120 deg and 110 Deg for a bidet

These are anti scald devices 1016-showers and 1017-distribution


The case I went against the NYCHA had the usual installation of a tempering valve with the 27" loop to prevent stratification of hot water entering the cold water supply but the victim was still scalded

https://pospislaw.com/wp-content/uploads/2013/08/Clinindin-v.-NYCHA.pdf

 

[TequilaMB]

Could it be the Intermittent Pilot Control module? https://www.supplyhouse.com/Honeywell-S8610U3009-Intermittent-Pilot-Control-4584000-p
Hubs remembers this was replaced once before. And DS and DD seem to remember that the hot water baseboard heater registers got overly-hot a few times last year before house heat was shut down for the season.

 

[TequilaMB]

Update: Our HVAC man came out and discovered a problem with the Relay on our boiler. It's an Emerson White Rodgers rbm relay 134-20103-301. He was able to clean off the contacts, and get it working, but said we should look for a replacement. I've been searching all over online, and can't find one. Does anyone know how I can obtain one of these beasts, or whether there is a replacement for it?

 

[Jadnashua]

That's a SPDT, 25A, max 277vac relay with a 24vac coil...unless it plugs in, any relay with those specs could be used as long as you get the new wires attached to the right terminals. If it plugs in, you'd need one with the same layout on the terminals.