Increasing upstairs temperature

[Vasquez]

Upstairs is 3-4° cooler than the living room, which we keep around 19° in the evening, the moveable thermostat (salus it500) is kept here. Trv’s are set to 4, which I believe is 20°.
I kept it upstairs for a day with trvs up there fully open and got it up to 17.8 on the landing but the boiler was on for a lot longer and the flow return temp was 56° ( flow temp set to 62°) so too high for condensing.
Vaillant eco tec 28kw combi, recently serviced and a chemical flush / magnaclean cleaned out of a load of crud. 8 radiators in total.
The bathroom seems especially cold, no trv and lockshield valve almost fully open, closing it to varying degrees has seemingly little effect, it cools down faster than any other rad but is also the smallest, 600 x 500 , it was never an issue with the old system boiler + HW tank.
Is the answer to put a much larger radiator in the bathroom? We can go taller but not wider, will that also help to reduce the return flow temp?
There is a good temperature differential across all the radiators, they all seem fairly well balanced.
How do I get the flow return temp down? Ideally under 50°

 

[flameport]

How much loft insulation have you got?

 

[Wayners]

Some things to think about.

Humidity in places like bathrooms can cause temperature change. Hard to heat a humid area vs dry.
I frequently run bathroom extractor and kitchen hood and I open bedroom windows for 10mins just to get rid of humidity in the house. I never yesterday and the moisture dumped on windows.
You can also get fans for radiators which heat up rooms better. The clip on the bottom..

It's difficult with weather so cold to get a really warm house unless it's a modern building with lots of insulation and air tight.

How's your isolation in loft

 

[Vasquez]

We have got a roll of insulation, it was meant to be put down over the bathroom area when we got the xmas decs down but the old cold tank is still up there and is in the way, it’s a very shallow loft, you can’t even stand in the centre, it’s less than 5ft high. I think there has been a bit of condensation up there, one of the boxes had fresh drip marks, the condensate pipe from the boiler runs across the loft floor next to the hatch, it’s pumped up from the airing cupboard.
The box room is warm, the radiator is about 30% bigger in there and it’s also got carpet and curtains.
The bathroom has vinyl flooring and is part tiled, part wall panels with a thermal blind. No drafts around the window and condensation disappears quickly after showers/baths, I use a window vac in winter on the shower screen etc.
There is a tiny bit of black mildew forming above the window on the ceiling.