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Vitodens DHW priority question
in Gas Heating
If the radiator circulator is running and the DHW aquastat calls for heat, should the radiator circulator immediately turn off? Mine kept running for a while, so both circulators (DHW and radiator loop) were going simultaneously.
if you need priority, you need interlock heating relay RA889A-1001 with DHW relay RA889A-1001 as described on page 32 of 5368 828 v1.6 manual
Installation and Service
5368 828 v1.6 11/2010
for use by heating contractorGennady Tsakh
Absolute Mechanical Co. Inc.0
I was under them impression that DHW priority was essential, but it looks like it is optional.0
If you zoned with Zone valves and used an exp version Taco Zone Control wire the system pump as a system pump to the zone control, plug in the Taco PC600 card in the power port on the zone control. Make sure priority switch is on. Take the XX on the PC600 card to DHW on the Vitodens, then take the XX on the zone control to RT.."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."0
My system has a single heating zone, so there are no zone valves (if that's what you meant). It is not currently set up for DHW priority, but the installer said the Taco relays he used will support that. If I understood him correctly, DHW priority can be switched on or off at the relay, but is currently off. Perhaps I misunderstood.
I'll see how it goes during the heating season. It is a small house (heat loss 33,000 Btu) and the DHW demands are not unusually large, so we should be OK.
The installer mentioned one potential drawback of DHW priority. If the DHW circulator breaks and can't supply heat to the DHW tank, the aquastat will keep calling for heat, and the DHW priority will keep the heat to the house off. If you are out of town when this happens, you could have pipes freeze.0
The boiler know tomgo into high fire? What Taco Relay did he use?"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."0
Does the relay tell the boiler to high fire for DHW, or does the boiler have on board logic to do that? When the DHW calls for heat, should the boiler always be at maximum fire?0
It Sure Should
Boiler should go to high fire on a DHW call. Something is missing from the picture. You have 1 zone of heat and 1 zone for DHW. If you have 3 pumps, boiler, zone and DHW cannot be using a single zone relay. Boiler pump is wired to pump on boiler control, Heating pump relay to RT and DHW relay to DHW. Do you have 2 SR501's?"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."0
Two SR501s. When the aqua stat calls for heat, the boiler's display indicates DHW (little faucet icon). The boiler initially fires at full input, then ramps down as the water temp approaches 176 degrees. According to Viessmann, this is normal operation.0
This discussion has been closed.
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