Fun with the furnace!

[NutmegCT]

Hydronic baseboard oil furnace heating system, with tankless coil domestic hot water.

Took my shower and all was fine.

Turned on hot water for washing dishes, water came out hot, then warm, then around 80F.

Furnace shows tankless coil is 140F.

Raised room thermostat to 90F, furnace came on and began circulating hot water through the baseboard pipes.

But even when the furnace is running, there's no hot water coming into the sinks, bathtub, or shower.

Turned hot water mixing valve all the way to max hot (160F) - still no hot water going to domestic outlets. Turned it to minimum (120F), no change. The outlet from the mixing valve is only around 80F, altho' the water in the coil is 140F.

I'm guessing the mixing valve is stuck - even tho' it's only a few months old. Hit the valve a few times with a hammer, no change.

Any suggestions?
Thanks.
Tom M.

 

[George_H]

Put in a tank and add a zone valve and you will never look back. Something is wrong with the mixing or the control for the mixing valve. Do you have hard water?

 

[NutmegCT]

Thanks George. I turned the mixing valve knob a bit, and water began spurting from the valve seal . That was about two hours ago. I turned off the furnace power. That started a leak at the DHW outlet from the furnace tankless coil to the mixing valve, so I've now shut off the water to the furnace also.

Water here isn't hard. Now waiting for emergency furnace crew to show up.

Furnace is 25 years old - time for a new one.

System has 3 zone valves already, which work fine. Say, why do you recommend a water heater tank instead of the tankless? Keeping 50 gallons of water at 120F seems fuel inefficient compared to a small tankless "demand" system with a much smaller static capacity.

Thanks.
Tom M.

 

[George_H]

I had one put in 30 years ago and have not had to touch it. They are well insulated now and are efficient. Many people in our area had those on demand systems and they give people problems. Mostly because on hard water messing with the mixing. Where I live we have very hard water.
We had natural gas come down my street last year. No more oil for me. Brand new gas furnace. I'm a happy camper!

 

[NutmegCT]

 

[mikephillips]

I replaced a 20yo gas furnace last year right at the start of the pandemic, got it as a cheap addon to replaces a 30+ yo a/c unit. It's one of those 97% efficient types with a plastic flue pipe. Now in the past during winter I'd turn it back when I went to bed and didn't turn it back up till I got home from work around 4pm. Now with WFH due to the virus I'd turn it up about 6am when I'd get up and it would be at the regular temp all day long. I've noticed, no real increase in the gas bill last winter even with it running more than twice as long each day. So a modern replacement certainly was worth doing.