Boiler temp for UFH/Rads (Condensing Combi)

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David_Dublin

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Hi All - we have done a full retro/refurb and have fitted a Veissman combi to run the hot water (DHW), UFH downstairs (wall stats), rads upstairs (rad stats plus 1 wall stat).

At the boiler I've the DHW and UFH/rads set at 46 degrees.

UFH is on "all the time". Rads come on for an hour in the morning, a few hours in the evening. I'm finding the UFH great, no issue there, downstairs set to 20 degrees and everything performing well.

Upstairs with the rads is hard to heat, it never gets near the 20 degree wall stat setting (stat is in north facing & biggest bedroom).

I am wondering should the boiler be set to run at higher temp: so the rads get hotter upstairs, but also I'm reading about 50 or 55 degrees is the optimal flow temp for UFH. Is 45 degrees too low for optimal performance for condensing combi with UFH?
 
If there is a possibility of legionella in your water supply, you might need a temperature of 55 degrees for domestic hot water.
 
I'd recommend having a read of this. It covers recommended temperatures.

You can adjust your hot water temperature somewhat, but you must be mindful of legionella risks. Legionella is a bacteria that can occur in domestic hot water systems. It is more common in stored hot water, i.e. hot water cylinders, although still very rare (see section 12 for more on hot water cylinders). There is a lower risk of legionella occurring in domestic dwellings that have a combi boiler (i.e. no hot water cylinder) and where there is daily usage of hot water.

https://www.theheatinghub.co.uk/articles/turn-down-the-boiler-flow-temperature
 
With undefloor I wouldn't go higher than 45 for the ch. If you find the upstairs is cooler than desired then check for heat losses such as air leakage (draughts) and address where possible and / or heat the space for longer.
 
On the boiler can you set different temps to UFH and rads or is that just one setting?

If you can't have different temps for UFH and rads you need a mixer valve for the UFH so it can run cooler than the rads. That mixer valve would be alongside the UFH manifold.

If there is a mixer valve (no guarantee it's been installed in my experience) it needs to be set to lower the temperature to a UFH level - it allows you to run the rest of your system at a higher temp.
 
ashambles said:
On the boiler can you set different temps to UFH and rads or is that just one setting?

If you can't have different temps for UFH and rads you need a mixer valve for the UFH so it can run cooler than the rads. That mixer valve would be alongside the UFH manifold.

If there is a mixer valve (no guarantee it's been installed in my experience) it needs to be set to lower the temperature to a UFH level - it allows you to run the rest of your system at a higher temp.
Click to expand...
Just one setting for rads and UFH, with separate setting for DHW. Mixer valve has been installed, so I have flexibility in what I set it as, it's been well installed. I just wanted clarity on optimal temp for the condensing boiler settings really.
 
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