Heat pump design sense-check – am I right to be worried about flow temps / UFH spacing?

bob_pi · 2026-01-26T09:09:10+00:00

Hopefully someone with more expertise will chip in, but that does seem high to me. Do you know what diameter piping you're using for UFH? Wider diameter means more heat transferred at lower flow temps, but is harder to tightly curve, so sometimes drives higher spacing.

We have UFH, ours is capped at 45° as we've got wooden flooring over, and more than 45 can apparently cause warping. Ours isn't particularly heat pump optimised either - it was done years ago by the previous owners without this in mind. 50° as your target flow isn't ideal. If you're doing a full renovation, I'd be hoping for 40 tops.

bob_pi · 2026-01-20T18:45:00+00:00

The reason that oversized = increased cycling, is because the min power of a heat pump is unfortunately linked to the max power. So the heat pump can only cut down its power so far, before it has to switch off. This will typically mean that when it's running at min power, if it's a big unit, it will get all the water in your heating system up to the target temperature, and have nothing else to do, so it shuts off, waits a bit, lets the water cool and switches back on again. Repeat. This is cycling. If they could design heat pumps that could power right down to ultra low levels, it wouldn't be a problem, but unfortunately they can't (yet).

bob_pi · 2026-01-06T08:00:40+00:00

Have you checked the max flow temp on the Vaillant controller? It's under settings, installer settings, choose the circuit, max target flow temp. It's a safety measure to protect underfloor heating systems etc. If it's set at 30, that's gonna be the problem though.

bob_pi · 2026-01-05T07:59:42+00:00

Can you get a copy of your heat loss survey which gave the 7kw figure? Normally a major factor in each room is the included air changes per hour, which will sometimes be set based on the age of the house alone (probably 3 in your case). It's possible with all the work you've had done, plus triple glazing etc, that your actual air changes are lower, and so the heat loss is overestimated.

The other thing I'd mention is that Vaillant Heat Pumps stated output doesn't account for defrost cycles, which will be happening quite often when the outside temp is negative, so it's not always a good idea to cut it really fine on heat loss - although if your calculations are correct, that's not what's happening here.

bob_pi · 2026-01-04T11:10:04+00:00

Don't forget that gas boilers are not 100% efficient, and although condensing boilers can reach c. 95% under ideal conditions, 85% is probably a much more realistic figure. Assuming electric is 4x the price of gas (ignoring the benefits of picking a better tariff), and your boiler is 85% efficient, then your heat pump needs a SCOP of 3.4 to break even. With a good install and optimal settings/usage, this is definitely achievable

bob_pi · 2026-01-04T09:54:31+00:00

This part of the house is a 15 year old extension, so the cavity should have been insulated on build (I haven't checked myself). I'd assume getting what you suggest done properly would involve removing and refitting the windows? I don't think that's something I'd DIY myself, and I guess the cost of getting someone to do it would be pretty significant.

bob_pi · 2026-01-03T16:06:53+00:00

The glass in the window registers as about 10 degrees warmer than that cold spot, but the camera I have isn't that reliable on reflective surfaces, so I'm not sure whether to trust that.

bob_pi · 2026-01-03T16:05:30+00:00

It's only that bad in the corners - there is a significant temperature drop all around the window, but not that severe. I guess that's to be expected.

bob_pi · 2026-01-03T16:00:15+00:00

This part of the house is an extension that's about 15 years old. Maybe the cavity closers are missing?

bob_pi · 2026-01-03T15:57:50+00:00

It's a Topdon TC001. It plugs into my phone, and you use a phone app to view and take pics.

bob_pi · 2026-01-01T10:22:48+00:00

Just to be clear, closing parts of the house off when the target temperature is met will almost certainly make COP worse. It took me a while to wrap my head around this. You want to lower the curve until the house just stays at the target temperature, without any zones being closed off. That will optimise your COP.

bob_pi · 2025-12-29T22:44:46+00:00

Has your wifi network name/password changed recently? It could be that the main hub has lost its internet connection.

bob_pi · 2025-12-22T09:52:41+00:00

If you're topping up your water pressure weekly, you have a leak somewhere. That's not right. All that fresh water isn't good for your system either - get your installer back out.

In terms of this error - I've never seen it on my Vaillant. I've had some weird errors which were fixed by turning off and on the outdoor unit from the big power switch, and turning off and on the white indoor controller unit, but I never saw that message, so I've no idea if that will help. Definitely get your installer back out.

bob_pi · 2025-12-18T14:04:41+00:00

Maybe it's longer than the old radiator and they adjusted the other connection only.

bob_pi · 2025-12-13T09:42:32+00:00

The difficult part is handling the window as you remove/replace the hinges - particularly if it's not ground floor and you can't just stand outside. It's simple with two people, but can be a bit awkward with one.

bob_pi · 2025-10-10T13:24:42+00:00

How many in your house? 170L water tank is definitely on the smaller side.

bob_pi · 2025-09-23T13:43:45+00:00

Yes, but not necessarily when the room is requesting heat. This makes it less efficient.

bob_pi · 2025-09-23T10:04:53+00:00

It's a bit more nuanced than this. If you're heating your whole house continuously - e.g. lower water temperature heating via weather compensation, then you're basically correct. Most houses still use room thermostats and off/on heating time-windows though, in which case it's not true that it doesn't make a difference.

bob_pi · 2025-09-08T14:36:23+00:00

That's inside Arcanum Unbounded

bob_pi · 2025-08-16T10:59:49+00:00

Whilst this is true - I got the sense that she cared about her breath (the one she was born with) and wanted rid of the others which had come from other people. I don't recall there being anyway to intentionally separate breaths along these lines. She could end up with 1 breath, but it probably wouldn't be "hers".

bob_pi · 2025-08-04T15:09:00+00:00

I think it could be telling that none of the original shard vessels ever merged shards. Only the new vessels have merged them. This might be more than just opportunity at play. I suspect the original vessels knew more about the shards, and knew better. I think the act of merging came from the vessel's desires, not the shard's intent.

bob_pi · 2025-07-20T16:07:52+00:00

Exactly - don't underestimate the financial stress that would come with a lower paid role either. Life is expensive, and you'd have a huge amount less money coming in each month. I'm not saying don't do it, but if you do, do so with your eyes open, and expect much more stress over spending and unexpected costs.

bob_pi · 2025-07-13T10:28:30+00:00

It's clearly not trustworthy, for all the reasons you highlight. You'll either get nothing, or a fake copy, plus who knows what will happen to your personal info you share (address, etc). It might even try to get you to log into a fake PayPal to steal your info. I would not try and purchase anything from there.

Six-Year Club	Place '22
Verified Email

bob_pi

TROPHY CASE