Inadequate hot water from domestic coil SOMETIMES.

[carnot]

I have a V8 series Burnham oil-fired boiler with domestic hot water coil, controlled by an L8124C Honeywell Triple Aquastat. About 80% of the time the domestic hot water is plenty hot -- more than fine for a shower, but about 20% of the time it's not hot enough; in these cases I have to turn the water off, wait a minute or two and then turn it back on -- at that point it will be OK (the burner has fired up). This has been happening during the summer, so cold water returning from the house heating system is not an issue here. I suspect that the aquastat has become flaky but would be interested in opinions from people with some experience.

[firecontrol]

Sounds like you're catching the aquastat just before the boiler is cool enough to bring the boiler on or you're drawing more hot water during these instances than the capacity of the coil. Either way an increase in the setting of the aquastat to bring the boiler on at a higher temperature might help the 20%.

[glennwith2ns]

Do you have a mixing valve on your hot water?

[black #1]

Have you considered a hot water storage tank and recirculating system?

[dna]

I was thinking mixing valve also.

[Freezeking2000]

Raise the temp if you need to so it will not get so cold before the boiler fires up. I would look at the manual for the proper temp setting with a coil. I keep my NewYorker steel at 220 degrees Hi/ 20 Diff.

[carnot]

First, thanks for the replies.

Mixing valve: Where you might ordinarily find an automatic mixing valve there is a ball valve, but it is closed.
Given that there is no mixing valve I have the high set at 170 (with a diff of 15). If I go higher the domestic water can be scalding.

The troubling aspect here is that it isn't OK all the time or not OK all the time. I may try raising the temp on the control and use the ball valve to introduce some cold water. I have found that controlling flow using that valve is difficult, however. (There used to be a gate valve there, but it failed giving me cold showers all the time and the service tech replaced it with the ball valve.)

[beenthere]

Have a mixing valve installed.

The ball valve won't be able to compensate for a heating call, and your water will become scalding hot many times during the winter.

[johnsp]

Is the low limit set too low? You should be at least at 130° or so since the boiler won't kick in until it drops to 120°. You might have the boiler dropping down below 110° before it can catch up. This could be causing some condensation in the boiler. An aquabooster tank or indirect lets you store up some hot water for sudden large demands.

[Edited by johnsp on 10-09-2006 at 11:56 AM]