Vitodens - External Call for Heat

Paul Pollets

You can't set up the Vitodens for "external call for heat" without using a 3 way for the radiant zone off the LLH. Circuit "B" is always the mixing valve.

The boiler will fire to 167 when calling. You can enable or disable the DHW priority.

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Man with a question

Vitodens External Call

Who has used the Vitodens "external call for heat" function?

I know this call connects on the 4.1 terminal in the comfortrol. My question is:

1) What temp water does the boiler output on an external call for heat? Does it go automatically to high fire? Does one program in the temp in the Heating Circuit B function?

2) Does an external call have priority over a DHW call?

My scenario is a Vitodens 15-60 with a low temp radiant circuit, a DHW tank, and a tube and shell HX for Spa Hot Water Production. I'd like to do this without the Viessmann Mix Valve set up if possible.

I'd like the priorities to be DHW, then SPA heating (It should only take the boiler about 10 minutes to heat the solar pre-heated spa), then Radiant.

What say ye?

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Man with a question

Well then

Thanks Paul,

So an external call does indeed put the Vitodens to hi-fire.

In that case:

If I retain the code for DHW priority, I get DHW priority.

I should only need the external call for a short period of time. How about turning off the Radiant secondary circulator via a NC relay during a high fire external call?

Then I get DHW, then Spa, then Radiant priority without the whole mixing valve.

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Paul Pollets

Maybe...

You can try it, but I suspect you'll need the mixing assembly.

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scott markle_2

The target temperature for external demand is adjustable via a coding address- OA2. Pretty sure my system which runs off a Tekmar steam control via the external demand contact, does maintain DHW priority during these demand periods.

Pulled out the manual- OC5 has 11 possible configurations which relate to external demand for heat. the last six of which leave the operation of DHW in normal control mode.

Did you know you can adjust the maximum firing rate in heating mode via a potentiometer on the lgm board, I don't think this is in the manual, mine is set to the lowest possible setting, DHW overrides this and the burner fires within it's full operating range when a dhw call is present.

If your using a Vissmann mixing valve (extension kit) OC5 has a setting which will close the mixing valve and turn off the circ. during the external demand. Looks to me like your going to want OC5:008. This setting leaves the heating circuit pump (primary) in normal control operation closes the mix valve- turns off the mixing circuit circ. and leaves the tank heating circ. (which for a 6-24 is the same as the heating circ.) in normal operating mode.

I really love this boiler, just noticed another thing that separates it from the pack. It has a flapper on the fresh air intake that limits convective standby losses. Unless something is wrong with a recent TT instal I noticed that this boiler has a post purge after every burner cycle. This combined with the lack of any check valve to prevent the flow of outside air through the boiler during standby seems to provide a meaning full conduit for stray BTU's. This is the sort of stuff that doesn't show up in an AFUE but sets Vissmann apart in their dedication to product efficiency.

justme_14

External call

On an external call DHW will not have priority! You can program the boiler to operate the DHW pump during external call for heat via coding address 0C5. The boiler will not necessarily goto hi-fire. The boiler logic decide if hi-fire is necessary.