Vaillant Unistor 310 —reduce capacity?

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I have a Vaillant Unistor 310 hot water cylinder which is used with a Vaillant ecoTEC Plus 637 boiler.

There are now fewer occupants living in the property, and so hot water usage is reduced.

It takes quite a while for the Vaillant Unistor 310 to fully refill during various times of the day, which interrupts the boiler from the central heating.

It is possible to reduce the filling capacity of the Vaillant Unistor 310 so that the boiler can return to the central heating faster?
 
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1. You can't reduce the capacity.
2. You could try setting the programmer so that hot water and heating are never on at the same time. For example, hot water on at 06:00, off at 07:00. Heating on at 07:00 off at 09:30. Similar in the afternoon / evening.
 
If you have thermostatic showers, you could reduce the cylinder temperature, which would mean it heats up faster. This would result in a higher hot to cold ratio when using the shower, so the hot water would run out quicker.

You are constrained by having to have the cylinder heated to 60 degrees due to legionella, but if you have vaillant controls, I believe they have an anti-legionella program, which means you could set the cylinder temperature even lower.
 
Thank you for the responses, seems I don't really have any options then...

oldbuffer said:
1. You can't reduce the capacity.
2. You could try setting the programmer so that hot water and heating are never on at the same time. For example, hot water on at 06:00, off at 07:00. Heating on at 07:00 off at 09:30. Similar in the afternoon / evening.
Click to expand...
...Already have done this, but there are occasions of overlap where both heating and hot water are required together, i.e. in the evenings.

fezster said:
If you have thermostatic showers, you could reduce the cylinder temperature, which would mean it heats up faster. This would result in a higher hot to cold ratio when using the shower, so the hot water would run out quicker.

You are constrained by having to have the cylinder heated to 60 degrees due to legionella, but if you have vaillant controls, I believe they have an anti-legionella program, which means you could set the cylinder temperature even lower.
Click to expand...
...Already have the water set to heat to 50 degrees.
 
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The recovery time [to 70%] for a 310 is 30 minutes.
If your boiler can't reheat the entire cylinder in an hour, something else is wrong.
 
Might be worth monitoring the boiler status codes...getting heat out of a 637 is often an issue.
 
If you have a VR65 (or similar Vaillant control center), there is a setting to allow both heating and HW at the same time. The cylinder will then take longer to heat up, but you won't lose heating - as long as the HW circuit is balanced accordingly.
 
copea said:
The recovery time [to 70%] for a 310 is 30 minutes.
If your boiler can't reheat the entire cylinder in an hour, something else is wrong.
Click to expand...

Yes, it takes under an hour to refill the 310, so no problem with reheating. But still quite a long time without heating in an old drafty house!
 
fezster said:
If you have a VR65 (or similar Vaillant control center), there is a setting to allow both heating and HW at the same time. The cylinder will then take longer to heat up, but you won't lose heating - as long as the HW circuit is balanced accordingly.
Click to expand...

Interesting. I have both the VR65 and VC430 installed but can't work out where the setting is to allow both heating and hot water at the same time.
Let me know if anyone knows how to enable this setting, it appears this ought to resolve my issue.
 
xxxx123abcxxxx said:
As per the instructions, I have set d.70 to 1 but the hot water still takes priority over heating.
Do I need a new compatible diverter value to use this setting?
Click to expand...

The 470 is a weather compensation controller so wont allow Parallel charging of cylinder and radiators.
 
The VR65 instruction manual explicitly states compatibility with the VRC400 series weather compensator.

However, you may be right about an incompatibility - I don't have personal experience. It does seem, though, that others have reported the "mid-position" not working when the VR10 thermistor is in use:

https://www.diynot.com/diy/threads/vaillant-ecotech-plus-418.197990/#post-1387163
https://www.diynot.com/diy/threads/hot-water-priority.302186/#post-2207977

OP - if you remove the VR10 thermistor and use the CYL connections on the VR65, you should find that it then works. But you will lose temperature control of the HW cylinder via the VRC430 and instead have to rely on the cylinder thermostat.
 
They are compatible. But the 470 is a weather compensating controller. Its never supposed to have a mid position option as it uses a different temperature on heat and hot water, not all features work with all controls. If you used a 350 controller (the non weather compensating version of the 470 then you can have parallel charging but then no weather compensation)
 
Just a suggestion for consideration by the panel...

Assuming the OP's system is using a VR10 cylinder temperature sensor, if a second VR10 sensor was installed so it was higher up the tank, with a switch to select which of the two sensors was the one in use by the VR65. Surely that would provide the OP with a means to reduce the HW capacity of the cylinder at will?

If the OP simply pulled the VR10 up some way out of the dry pocket, then that would reduce the HW capacity too, but with no quick easy means to restore full HW capacity.
 
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