Gas/Propane Basics
Timmie McElwain
President, Gas Appliance Service
timmcelwain@gastcri.com
Introduction to Modules Used
on Intermittent Pilot Systems:
Part 2
There are many differences between gas and oil
hydronics. The obvious one is that the burners
and fuels are different. The controls, however,
are typically the same—with some exceptions. In this
new series of articles, I am going to address some
of the differences and how to work with them. Our
emphasis will be on forced hot water and forced warm
air systems used on both natural gas and propane
systems.
We will be emphasizing the older systems and not
explore any modulating/condensing equipment. I want
to address controls that are unique to gas. As we look
into some more modern systems and what specific
problems they present, it is important to understand
the basic fundamentals associated with these systems.
Most of our modern heating equipment in some way
or another involves electronics and with the electronics
the use of flame rectification as a safety and flame
proving system. It does not matter if it is a forced
warm air furnace or a forced hot water boiler; the same
basic system is used to perform safe ignition and then
consistent operation throughout the entire call for
heat.
There are, however, different ways it is applied from
intermittent pilot application to direct spark ignition
and including hot surface ignition. Each has its own
distinct advantages and problems. In this next series,
we will provide corrections and diagnostics to help
solve those problems.
We will start with the basics and go from there into
operation, typical problems, diagnosis, troubleshooting
procedures and hopefully a final solution to your
particular problem. It is easy to jump to conclusions
with these systems and just change parts until you
hopefully solve the problem. That is, however, timeconsuming
and costly.
In our last article, we introduced the Honeywell
S8610U module. We covered the first module, which
was introduced in the early 1990s—it was a gray plastic
for identification and distinction from the modified
version, which is black plastic.
When to use the S8610U
Keep in mind there have been two modifications made
to the S8610U that we will cover in the next series of
articles. To identify which version you have, the original
modules were all gray plastic cases. The two later
versions had black plastic cases. Shown in Figure 1 is
the latest version the S8610U-3009.
It is recommended to use cross-references that are
Figure 1
Honeywell S8610U-3009
available from Honeywell. There are typically more
than 250 modules that can be replaced by the S8610U.
While cross-references are rather extensive, they
should not be considered inclusive. The original gray
casing model S8610U can be applied on virtually any
system that has a pre-purge less than four seconds
long and a trial for ignition at least 30 seconds in duration.
The module meets requirements for 100% shut
off. As always, pay attention to specific system requirements
and possible modifications if required before
installing a replacement module. If a control you are
looking to replace is not listed in the cross-reference,
check with Honeywell before replacing.
The S8610U should not be used to replace controls
that have lock-out timing less than 30 seconds or that
have pilots with ratings above 1500 BTU/hour. These
specifications are typically found on appliances used in
commercial applications and are regulated under different
standards than those that apply to the S8610U.
Using the S8610U on such appliances is outside its
design parameters.
The newer versions of the S8610U have a black plastic
case for identity purposes to differentiate them from
the original S8610U gray plastic. The newer S8610U
has a 3009 number also as part of its new identity.
Look for an S8610U-3009 as a direct replacement
today. The differences between the old and new will be
pointed out in these articles.
S8610U Installation
See Figure 2: Installing the S8610U.
• Enclosure has one open side and five sealed
sides—like a cup.
18 C M / S e Iptember/October 2019