Summer Hot Water, Winter, not so much

JimF

I have a Utica SFH3100WTL boiler. It was installed summer '12 before we purchased the house that fall. During spring/summer/fall we have plenty of hot water. In the winter months - after we turn the heat on - the more the boiler runs to heat the house the more lukewarm & less plentiful the hot water becomes. This has been going on for the last 4 years. I had a serviceman look at it but all he did was turn the mixer valve up a few degrees. I've got a feeling there's something else going on. I tried contacting Utica but got no response. Any advice?

SWEI

Do you have a tankless coil in the boiler? If so, it may need descaling. It could also be undersized, in which case a buffer tank can be added to cover the gaps.

JimF

Excuse my ignorance but I have no idea if there's a tankless coil in the boiler or not. I was told there's only a 2-3 gal HW tank in the boiler itself but I can't get past the fact the during the warmer months I have plenty of HW. Could it be that during the winter the water coming in from the street is so cold it can't be heated fast enough? I'm in north-central MA and my setback from the street is probably 100'.

STEVEusaPA

Yes you have a tankless coil. Yes colder water coming in means the hot water will be...less hot. But it's usually indicative of what @SWEI said. I have a few customers that don't get enough hot water around the end of a week long deep freeze.
You can look up how to clean out a coil, internally and externally on youtube.
You may also have other problems/considerations.
1. Flow rate of fixtures. High flow rate in shower means the boiler may not be able to keep up
2. Mixing valve blocked, starting to fail. Mixing valves fail to the cold.
3. Aquastat control. Maybe the aquastat isnt sensing the correct temperature. The low limit could be too low, or could be set 'right' but not sensing the proper temperature.
What are the settings on your aquastat, and can you confirm the temperature set is the actual temperature of the water.

JimF

I believe this is the mixer valve, but I wouldn't know an aquastat if it bit me in the butt.

JimF

Our shower head is new within the past 4 years & is one of the low-flow ones. When you say check the water temp, do you mean just run water at the tap & stick a thermometer in it?

Solid_Fuel_Man

I wonder if the boiler is on outdoor reset, and during heating the temp is lower. Therefore not good DHW production.

@JimF you really should look into having an indirect water heater installed. Will save you much fuel in the non heating season.

Taylor

bob eck

Do you have hard water if so clean the coil.
If you are running out of hot water in the winter it might be that your thermostat is calling for heat and the circulator is running and most of the hot boiler water is getting pumped out into your heating system and thus there is not enough heat transfer to heat your domestic hot water in the coil. You can check this by turning your thermostat down by 5 degrees and then showering. If you do not run out of hot water with the thermostat turned back your problem is your boiler is sending all the hot boiler water out into your heating system. In the spring, summer and fall the heating system is not calling for heat so the boiler keeps the hot boiler water in the boiler and you have pleanty of hot water to shower with.
If I were you I would install a indirect water heater and then you will have 35 - 40 gallons of hot water with about 150 to 170 gallons per hour or about 2.5 to 3 gallon per minute and your heating contractor can give the indirect water heater priority for domestic hot water so the heating system and indirect water heater are asking for hot boiler water at the same time your indirect water heater gets priority first so you do not run out of hot water. They can also make your boiler a cold start and this can lower your oil bill.

JimF

Thanks gents - this is a lot of good information to go to my local guy with.

Zman

The summer vs winter is a bit odd.
What kind of heating do you have? In slab radiant?
There should be a temp gauge somewhere on the boiler. It ought to be in the 160-180ish range. What does yours say?

JimF

My heat is forced hot water with radiators. The temp on the boiler is a shade under 165 at the moment. It's after 11PM and my setback thermostat is now set at 62 so the heat hasn't been on for a bit. Plus it's now about 55 outside, whereas this morning it was about 24.

SWEI

Zman said:

The summer vs winter is a bit odd.

Tankless coil, possibly limed up. Add cold winter groundwater and stir.