Problem with UFH

[Adsibob]

I unexpectedly had to wfh today for the first time in a couple of months. Normally, the heating in my office (loft conversion, now the top floor of an upgraded and fully refurbed 1930s house) works well. It is not that responsive, but that’s the compromise we made with having engineered wooden flooring. We run the water temp at 35C, which is the lowest our budget manifold will allow, and after some initial anxiety that this was too high for the engineered floor manufacturer’s recommendation, it’s worked very well and the floor is fine. This is our second winter in the house. But today, this is how slow it took to heat up:

 

I turned it on at 10:22am when it was 17.9C. It’s been on for the last 11.5 hours constantly and has only now reached 20.3C. The outside temperature at the moment is 4.5C and I think today the max was around 7C or 8C. You can see that before I turned on the heating, the room had already begun to warm up a little from solar gain and heat rising from the rest of the house, so the gradual temperature rise in the first hour at least had nothing to do with the heating being on.

 

 When I realised at 2pm that I was still wearing my coat and hat in my office I checked the thermostat and saw were only at 18.3C. At that point I checked the flow rate. It was at 2L. I tried increasing it to 3L. This didn’t really make any difference. About 9pm I tried increasing flow rate further, but turning the nut/valve didn’t do anything. I kept turning it until I accidentally pulled it right off and made a mess of water. Not that much, maybe 200ml or so max before I managed to screw the nut back on. That manifold has two other zones, each with one loop (so three different zones, each one with one loop). I noticed that the shower room on that floor was also failing to get to temperature, but on that flow valve, at least turning the nut increased the flow to 5L, the max on the gauge. But even at max flow, the bathroom took 3h to heat from 19.5C to 20C and we don’t have wooden floor there!

 

 So something is clearly wrong. 
 

The pressure gauge under my system boiler is showing 1 bar with everything off, and 1.3bars with a few zones on and the boiler running at 30% modulation and also 1.3 bars with almost everything on and the boiler running at 60% modulation. These pressure figures seem a bit low to me (I think normally when in operation it runs at about 1.6 bars) but it’s been ages since I’ve looked, and can’t remember.

 

 Any ideas? should I top up the water in my ufh to make up for the lost 200ml or so of water? How do I do that? Is it a tap on the manifold (pictures in further posts below) or just the way of topping up the pressure on the boiler?

 

[Adsibob]

[Adsibob]

And now some close ups of the gauges on the manifold:

 

[Adsibob]

Weirdly, I see that the water temperature gauge of the UFH manifold is showing 26C (looks like 25C on the photo, but camera angle is out). I will check back on my notes (buried on this forum somewhere) but I swear it’s not meant to go below 35C.

[JohnMo]

If you are flowing 35 after the mixer the temperature before the mixer should be warm to touch possibly hot - is it?

 

Flowing 25 downstream of the mixer looks more like cool water within the floor loops circulating.

[Adsibob]

35 minutes ago, JohnMo said:

before the mixer

Thanks @JohnMo but would you mind explaining, Sorry for my ignorance but I think of the whole manifold as “the mixer”. 
ok switching brain on, is this right:

A = after?

B = before?

Edited December 14, 2023 by Adsibob

[JohnMo]

The two grey pipes one will be supply hot water from boiler, the other cool reject water from the UFH mixer, back to boiler.

 

One pipe should be quite warm the other quite cool. 

 

A. and B. are correct. If you have the same temperature in both sections you are just circulating floor water

[Adsibob]

Thanks. The temp difference between A and B is definitely noticeable, but it is not huge. I turned the temperature up and now the gauge is saying the water entering the loops is in the low thirties, so could possibly increase it further, but I will leave it for the moment and see how I get on today.

 

 Do I need to top up the system to correct the small water loss I had yesterday when I lost about 200ml or so?

Edited December 15, 2023 by Adsibob

[JohnMo]

29 minutes ago, Adsibob said:

 Do I need to top up the system to correct the small water loss I had yesterday when I lost about 200ml or so?

If your boiler is happy and it must be as it's running, then it should be be ok to leave as it is.

[SimonD]

You are getting hot water flow to the manifold from the boiler aren't you?

 

Have you physically removed the actuators from the manifold to see how it flows then?

[Adsibob]

45 minutes ago, SimonD said:

You are getting hot water flow to the manifold from the boiler aren't you?

Yes

 

46 minutes ago, SimonD said:

Have you physically removed the actuators from the manifold to see how it flows then?

That sounds a bit advanced for my plumbing skills. What’s an actuator?

[SimonD]

3 hours ago, Adsibob said:

That sounds a bit advanced for my plumbing skills. What’s an actuator?

 

Those are the on/off valves for each of your ufh loops. They're the white things with red in the middle with the labels on the bottom rail of your manifold. Heatmiser UH8 wiring centre provides just relay control of the actuators so they're technically only on or off but can stick. So even though the UH8 has lights on for your office and bathroom in the photo, and the actuators look like they've opened, they might not be permitting sufficient flow. It may not be down to the actuators but just part of the overall problem solving process for any ufh with flow issues.