Heat works fine Shower takes over 10 minutes to "warm up"

[Rob McEachern]

I just recently moved in to a new place. We had the local service company come by and do the "Annual service".

The two heat zones (upstairs and downstairs) heat fine.

The shower takes over 10 minutes to heat up. The first minute or two the hot water in the shower is sufficient however after that the water gets cool and takes FOREVER to heat back up if at all.

The unit is a-
Burnham RSA Series Low Pressure Boiler
Model-RSA 85RH-TB

Honewell-Triple Aquastat Relay
Type-L8124A,C, L8151A

Is there an "easy fix"
If there is thread already about this please point me to it.

Thank you in advance.
Rob M. Milford MA

 

[Dana]

I'm assuming this is a tankless coil in the boiler, not an indirect fired tank(?).

If the low limit is set pretty low (140-150F) and the coil is getting limed up, the first slug of water will be what's been stagnating in the coil, and still plenty hot. But as you draw hot water the cold water entering the coil needs a bigger temperature difference to get fully up to the temp you're looking for. Only after the boiler has been firing for awhile does it reach a high enough temperature to deliver that hot water performance.

The easy solution (assuming the aquastats are operating correctly) is to raise the idling temperature of the boiler to 160F or even 170F.

The better solution is to install an indirect tank hot water heater operated a the "priority" zone, and idle the boiler at a lower temperature for lower standby loss, or even set it up for cold-starting (if that boiler is cold-startable- not sure that it is.)

 

[Sponsor]

 

[Jadnashua]

I had a tankless coil for my hot water...it got way too annoying, and I trashed it for another system - an indirect...much nicer. As your winter-time cold water temperatures drop, you'll find it to be even more of a pain. Might work fine in the summer. It wasn't worth the hassle to me.

 

[Dana]

The liming-up issues with tankless coils and their propensity to develop pinhole leaks make them a truly third rate solution to heating hot water in locations with wintertime incoming water as cool as those found in Milford MA.

Having to keep the boiler at 150F+ even in summer to get barely adequate hot water performance is another. A 68-70F boiler room might be OK in winter (if it's inside the thermal and air boundary of the house), but a 78-80F boiler room in summer is just piling on to the cooling load.

At least the RSA 85RH-TB is likely to be "only" ~3x oversized for the average house in Milford. The "85" is for 0.85 gallons per hour burn rate, x 138,000 BTU/gallon= 117,300 BTU/hr input, x 85% burner efficiency= ~100,000 BTU/hr output. A heat load of a typical 2x4 framed insulated 2000' house with some fluff in the attic and clear glass double panes (or clear glass storms over single panes) with no foundation insulation would run about 35,000 BTU/hr @ 0F, 40,000 BTU/hr if it leaks a lot of air. An older barely insulated antique might come in around 50,000 BTU/hr. Even the smallest oil boilers are oversized for the space heating loads in this state, taking a significant efficiency hit unless heat purging controls are used, to keep the idling and distribution temperatures & losses to a minimum. Can't use that type of control with a tankless coil due to the high idling temp requirement, but you can with an indirect.

Whether an indirect is really the right solution for the hot water depends on what, if any thermal or HVAC upgrades you intend to make on the place.