Viessmann Vitodens 100 Boiler

[Matttt]

Hi,
Moved in to a new house in April and had the boiler serviced the following month with no issues advised.
Have started using the heating now but have a problem that I can only get the heating to work if I turn the dial for the water off. As soon as I turn the hot water dial back on, it always heats the water and effectively ignores the heat.
With the water off, the heating acts correctly according to the thermostat, but then once the water dial is turned back up, the boiler constantly heats water.

Any suggestions will help! It's been suggested a diverter valve may be faulty?

 

[JohnD]

@Matttt
you have a hot-water cylinder, right?

If so, what colour is it, how long does the cylinder take to get fully hot, what is the temperature showing on the boiler, and what temperature is the cylinder stat set to?

Some photos of the boiler controls, and the pipework around the boiler and the cylinder, would help a lot.

There are several different models of the 100. If you have any documentation, it may say which you have, or at least its year. Look for a model like WB1A, WB1B or WB1C.

 

[Jackrae]

I believe the veismanns give priority to DHW (at least my 200 unit does) Does your tank have a temperature sensor fitted to 'tell' the boiler when the tank is hot enough so's it can terminate water heating and transfer heating back to CH. Sounds like your system is doing what it's designed to do - it's maybe a case of simply reading up on how your system works.

 

[jashton]

With DHW priority I assume there must be a temp feedback to the boiler, or does the boiler figure it out using the deltaT on the DHW loop?
Reason I ask is that I'm looking at getting a Veissmann Vitodens 100. I have Evohome installed and I have a Megaflo unvented cylinder. It's not possible to fit the Evohome DHW stat without removing the Megaflo's own stat to make room (given that the overtemp stat must be left in place and the Evohome thermistor is big andf fat and just fits. I therefore doubt it would be possible to fit another stat for the boiler's priority DHW stat, unless it was very slim/small

 

[Jackrae]

The 200 models use a resistive temperature sensor input , not a switching thermostat input.
Don't know about the 100 models but the installation/user manuals (available online) will clarify

 

[Agile]

There have been many different "100" models.

I have only seen the older ones and as far as I know none of those that I have seen have a facility to set the boiler flow temp separately for HW heating.

The 200 model has a separate diverter valve for HW heating and of course the facility for separate temps.

Without knowing the exact "100" model we cannot look it up!

Tony

 

[jashton]

It would be a new one. Not sure of capacity yet but a 100-W
Looking at some of the literature the 100-W definitely has priority by default but it is turnoffable. I haven't found any info yet about how it takes temp feedback. The install manual gives an example of a Honeywell aquastat being used but that's downstream of the boiler and just controlling separate DHW and CH pumps in sequence to handle priority.
i could choose to disable priority but am curious about how it works.
Also, having read some more recent posts about OpenTherm having very limited benefit I may not bother with it. That opens up many more possibilities of boiler choice

 

[DavidLewis]

There have been many different "100" models.

I have only seen the older ones and as far as I know none of those that I have seen have a facility to set the boiler flow temp separately for HW heating.

I have a Vitodens 100 WB1A system boiler from 2006ish. The boiler flow temperature is set by the knob on the front for the heating, but changes automatically to 80 degrees C while HW is demanded. That's because the heating thermostat and the cylinder thermostat are wired to their individual terminals on the boiler, as shown in the instructions. Perfect. The cylinder reheats really quickly and we never run out of hot water.

 

[Agile]

Hi,

Moved in to a new house in April and had the boiler serviced the following month with no issues advised.
Have started using the heating now but have a problem that I can only get the heating to work if I turn the dial for the water off. As soon as I turn the hot water dial back on, it always heats the water and effectively ignores the heat.
With the water off, the heating acts correctly according to the thermostat, but then once the water dial is turned back up, the boiler constantly heats water.

Any suggestions will help! It's been suggested a diverter valve may be faulty?

It would appear to me that your hot water cylinder thermostat is set too high or has become displaced from its position on the cylinder.

OR

To enable the cylinder to reach its temperature of normally 60 C, the boiler flow temperature has to be at least 10 C higher, otherwise the boiler will carry on trying to heat the water for ever.


Other's comments indicate that later 100 W boilers do have the facility for an input when there is a hot water demand which causes the boiler temperature to increase to about 80 C during water heating. But that requires the system to be wired to give hot water priority. That means the boiler only heats hot water and never both CH and HW together as in the normal Y plan.

Tony

 

[DavidLewis]

Other's comments indicate that later 100 W boilers do have the facility for an input when there is a hot water demand which causes the boiler temperature to increase to about 80 C during water heating. But that requires the system to be wired to give hot water priority. That means the boiler only heats hot water and never both CH and HW together as in the normal Y plan.

My boiler predates the "100-W" series. Yes, it's wired to give hot water priority (W-plan) - if the boiler is plumbed as a 4-pipe installation then the internal W-plan diverter valve is used by default. Mine's actually plumbed as a 2-pipe with an external 3-port valve.

It's my opinion that in well-insulated houses with quick-reheat cylinders (and especially with dual-temperature boilers), W-plan is superior to Y-plan, which still seems to be used too much for (I'm guessing) historical reasons? If nothing else, the external W-plan three-port valve doesn't have any of those blasted microswitches that are the cause of so many system malfunctions!

 

[Phill Peck]

With DHW priority I assume there must be a temp feedback to the boiler, or does the boiler figure it out using the deltaT on the DHW loop?
Reason I ask is that I'm looking at getting a Veissmann Vitodens 100. I have Evohome installed and I have a Megaflo unvented cylinder. It's not possible to fit the Evohome DHW stat without removing the Megaflo's own stat to make room (given that the overtemp stat must be left in place and the Evohome thermistor is big andf fat and just fits. I therefore doubt it would be possible to fit another stat for the boiler's priority DHW stat, unless it was very slim/small

You wouldn't need another sensor.
Use evohome sensor and viessmann change over hw box.

 

[Phill Peck]

There have been many different "100" models.

I have only seen the older ones and as far as I know none of those that I have seen have a facility to set the boiler flow temp separately for HW heating.

The 200 model has a separate diverter valve for HW heating and of course the facility for separate temps.

Without knowing the exact "100" model we cannot look it up!

Tony

The 100 system piped as 4 pipe as designed will