What's involved in a comprehensive annual service of a mod con boiler?

john123

Posters seem to say that the annual service for a mod con is on the expensive side. I can see if you have to do an hour-long? flush; that could add to the cost substantially. Perhaps one could learn to do the flush --and leave it on longer?-- so as decrease the expense but what else is involved with the annual service?

HomerJSmith

Water tube or fire tube? 1 to 3 hrs.

GGross

they can range in price based on your region, and the company doing the work, and of course if the boiler requires that seals etc be replaced when opening the burner, or if there are annual maintenance parts, some do require this, many do not. as homer stated 1-3 hours, plus the cost of any parts needed depending on several factors

Generally the tech should
visually inspect the unit and piping, including the vent (not specific to mod-con)
check fill pressure (not specific to mod-con)
check the expansion tank (make sure it is correctly charged and functional) (not specific to mod-con)
check incoming gas pressure (not specific to mod-con)
combustion analysis before and after service (not specific to mod-con)
open the burner compartment
clean the heat exchanger (this can be the bulk of time spent)
check the specification of the flame sensor and igniter (the gapping and distance to burner)
clean the condensate trap-refill trap
put it all back together and run the system while doing the final combustion analysis

I have the good fortune of generally only going to jobs that have persistent issues so my view on this is rather jaded, but I do not see many techs actually do a solid service on mod-cons. It is one of the reasons there are some who do not like them. They get to follow up on units that have never had a proper service and the problems can be hard to diagnose at that point.

john123

@GGros: do you always (every year) do a flush? with chemicals? with vinegar? and 1-3 hours depending on the type?

hot_rod

You do not want to change the water in the system every year.

Ideally the system is cleaned when installed and good quality water was used, not hard water! Good water, maybe with a hydronic conditioner should last 10- 20 years.

Also I have found a yearly inspection is not always required. If I open up a boiler, remove the burner cover, and inside it is whistle clean I'll go two years before another opening.

If you have a service contract, checking gas pressure and a combustion analysis tell most about condition.

If the system has glycol antifreeze, a ph test every few years is a good indication of the fluid.

EBEBRATT-Ed

If everything is in good shape and kept that way you can probably go every 2-3 years between pull apart and cleaning. A combustion check and a look see every year is a good idea.

john123

@hotrod: by "flush" I was not referring to changing the boiler water. I was thinking that you have to do a boiler flush (every year??) to remove as much of the crap inside the HX as possible. I thought you isolated the boiler and sent (pumped) the water with chemicals just through the boiler and back into the 5 gallon pail continuously for a hour or so and all the crap settled in the bottom of the pail. Does anyone do this?

HVACNUT

john123 said:

@hotrod: by "flush" I was not referring to changing the boiler water. I was thinking that you have to do a boiler flush (every year??) to remove as much of the crap inside the HX as possible. I thought you isolated the boiler and sent (pumped) the water with chemicals just through the boiler and back into the 5 gallon pail continuously for a hour or so and all the crap settled in the bottom of the pail. Does anyone do this?

Yes, the boiler is isolated from the system piping. Some manufacturers want 2 or 3 hours. We don't include it as part of an annual maintenance. An assessment will be made during the maintenance and if necessary, a return visit for the flush. Different manufacturers want different chemical solutions too so sometimes it needs to be ordered. 

hot_rod

john123 said:

@hotrod: by "flush" I was not referring to changing the boiler water. I was thinking that you have to do a boiler flush (every year??) to remove as much of the crap inside the HX as possible. I thought you isolated the boiler and sent (pumped) the water with chemicals just through the boiler and back into the 5 gallon pail continuously for a hour or so and all the crap settled in the bottom of the pail. Does anyone do this?

Maybe on an old iron pipe system, mor connected to old cast iron radiators would involve a flush occasionally.

To remove solids like dirt, rust flakes etc you need to get a good flow above 5 fps velocity.

A flush pump or connect directly to city water pressure is what you need to do to get that flow.

On a new system, copper tube, pex, etc, rarely should you need to flush the boiler HX.

The hydronic conditioners add a film provider to the piping and boiler and also keep minerals in suspension to prevent sludge build up.

I like adding hydronic conditioners even to good DI water fill. You get Ph balancers, film providers, O2 scavengers and additive to keep particles suspended.
A test kit will show you went to add a squirt of booster.
Rhomar, Fernox, Adey, Axiom etc for hydronic conditioners.

Every time you add any new water you add O2, which is what caused some of the corrosion problems to begin with.

GGross

john123 said:

@GGros: do you always (every year) do a flush? with chemicals? with vinegar? and 1-3 hours depending on the type?

The system water should be hopefully good from the start, in the closed loop system I do not advise changing out the system fluid annually, this will generally introduce new minerals into the system which can negatively impact the system over a long period of time.

As @hot_rod said there are times when flushing the system is a good idea, like an old system with lots of iron or if you already have sludge issues. Adding appropriate conditioners etc is a good idea as well.

If you have a "combi" mod-con boiler, that creates DHW via a flat plate heat exchanger inside the boiler, then you would really benefit from having the domestic side of that heat exchanger flushed with vinegar annually (not the boiler heat exchanger) These tend to scale up less than a typical tankless water heater, but they can still get some scaling or debris that impedes flow.

scott w.

My service provider said my Weil McClain mod con only needs service every other year. My technician does what GGross stated above. They check everything and takes about and hour and 45 minutes. They replace the ignitor. Cleaning the heat exchanger takes the most time. Cleaning the heat exchanger looks to me as one of the really key maintenance items of the regular maintenance. If let go looks like a major issue to clean down the road. The charge for service is a couple of hours of tech time. I provide the parts. I can get them cheaper than what service provider charges. Purchased quantity several years ago as the price kept increasing dramatically each time.

Paul Pollets

Labor costs keep rising and there is a shortage of trained technicians. Proper cleaning takes time and requires special tools. If the cleaning is ignored or done improperly, serious problems will occur and they tend to happen on the coldest Saturday night in December.