Servicing high efficiency modcon boilers

Many faithful readers of my column know that I have a modcon boiler in my home. In fact, as soon as I get done with my special project in the mountains (Hydronicahh), I will have a mod-con boiler in all of my homes. More on Hydronicahh later When I installed the Gianonni platform boiler in my own house, I also installed the instrumentation necessary to monitor the net thermal efficiency of the boiler.

Many faithful readers of my column know that I have a modcon boiler in my home. In fact, as soon as I get done with my special project in the mountains (Hydronicahh), I will have a mod-con boiler in all of my homes. More on Hydronicahh later…

When I installed the Gianonni platform boiler in my own house, I also installed the instrumentation necessary to monitor the net thermal efficiency of the boiler. I have an extremely accurate flow meter on the hydronic side, an NIST approved gas meter on the fire side, and solid state thermistors on the water side. When it was originally installed, it had a net thermal efficiency of 95% when on high burn, heating a cold tank of domestic hot water from scratch. I had a verbal agreement with the manufacturer that I would intentionally not service the appliance on a regular scheduled basis, but instead would check it three or so years later to see how it was doing on thermal efficiency.

This winter was the third year for this particular appliance and it was time to put the stethoscope on and see how healthy the patient was. When I did so, I was shocked and dismayed. The appliance had gone from being 95% thermally efficient down to being only 60% thermally efficient.

The wife said she had noticed an increase in our energy bill, but had concluded in her mind that all energy costs were up, so she didn't bother to say anything to me. I don't usually see our energy bill unless I ask for it. I had assumed that we had the most efficient gas fired appliance available and that there was no real need to worry. Boy was I wrong.

It was time to roll up the sleeves, drag out the tools of the trade, open the patient up and see what was going on inside. Upon opening the appliance, I found that there really was as much crud built up on the heat exchanger as I would have thought there to be based on the deviation in thermal performance. In fact, if someone had shown me pictures of this heat exchanger, I would probably have told them that it wasn't really in that bad a shape and could probably skip servicing the heat exchanger on the fire side. I have seen much worse conditions in the field.

The boiler is a Gianonni France-based appliance. The sub-manufacturer recommends the use of a product called CLR, which is a product for removing calcium, lime and rust. I recommend removal of the dry products of combustion first. Then vacuum those dry components out. This part of the task sounds easier than it actually is. The dry products of combustion are extremely hard, and the manufacturer does not recommend the use of any steel tools (use only nylon, stainless or brass brushes) to loosen this material. Once this task is done, I recommend either removing the back fiber ceramic target wall or cover it with an aluminum pie pan to keep it from getting wet. A word of caution here. The fiber ceramic target wall, once exposed to intense heat, can emit dust particles that are carcinogenic. Be certain to follow the manufacturer's recommendations in regards to safety practices, protective clothing and protective breathing apparatuses.

The next step involves removal of the condensate drain line and repositioning it for visual confirmation of flow. The manufacturer recommends spraying the CLR concentrate on the heat exchanger area, allowing it to soak in for a brief period of time, approximately 15 minutes. Then vacuum the loosened clinkers out of the combustion chamber. After that, carefully rinse the cleaned and scrubbed area of the combustion chamber. I would recommend the use of a water vacuum connected to the condensate drain hose to suck the small particles out of the condensate drain area. This insures no partial blockages will occur in the condensate drain system. It might be necessary to back flush the condensate drain hose with pressurized water in order to establish a good flow through the condensate pan and drain assembly.

It is probably going to take more than one CLR application in order to cleanup the heat exchanger. I used three applications to get the heat exchanger looking like new. It has been my experience that no two boilers accumulate the byproducts of combustion the same. The only commonality of extremely dirty heat exchangers I have seen is in areas with a lot of air pollution. It seems that these appliances get dirtier in a shorter period of time than one located far away from the dust of the city. However, I have experienced clogging in rural situations too. I had a boiler at an equestrian center, whose air intake was 30-ft. above grade. It was plugged with a mud that smelled of horses. We installed an in-line air filter on that appliance, and the mud disappeared.

Tune in next month as we continue our journey through the combustion chambers of time. … Until then, happy service-oriented hydronicing!

Mark Eatherton is an independent hydronic/alternative energy heating systems consultant. He can be reached at [email protected].

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