MJNewton

I've always been so disappointed with the performance of LEDs and whilst they've got a lot better over the years I still don't consider them anywhere near as good as halogen in terms of their dimmability, changing colour temperature when dimmed (which I like) and colour rendition. Of course, they win hands down in running costs so I've somewhat reluctantly gradually moved over to them. Finding halogen-like GU10 replacements has been particularly difficult with disappointment after disappointment from brands I'd expect more from (eg Philips/Signify) but am pleased to say a few months ago my seemingly-eternal search concluded with the Civilight CL 5620 from well-lit. CRI of >95, dim-to-warm, anti-glare light source, built-in heatsink and a 3yr warranty. They're expensive at £13.98 each but, frankly, I got to the point where I couldn't really care less as I wanted high quality light output and nothing else was coming close. Hopefully they'll last longer than 3 years (they're rated at 25,000 hours, which is roughly 3 years of constant usage) otherwise the payback might be slim compared to the halogens they're replacing but we'll have to see. They're not perfect halogen replacements, but they're the best I've found at satisfying my requirements and subjective preferences - and they're good enough for me. One thing that helped me take the risk was their 1yr 'money back guarantee' which basically says if you don't like them you can return them within a year and get your money back. I happened to be discussing lighting on a DIY sub-forum on a car forum (like you do) and mentioned I was going to try these and wondered if anyone else had, and whether they'd had any experience of this guarantee. Much to my surprise the owner of the company happened to be on the same forum so he piped up and came across as really genuine and clearly *really* into quality lighting (that was why he'd set the company up - had basically gone through what I had but rather than just moan on forums decided to do something about it!). He said they offer that guarantee because the bulbs he sells are that good - they hardly get any returns so it's minimal risk for them. Incidentally, he too recommends the Varilight Pro (at least for non-smart control - he's more into pricey smart controllers) and these bulbs are completely stable even down to virtually zero output.

I think the calculations are *definitely* still worth it as it'll give you an idea what minimum flow temperature we need to be aiming for. Furthermore, it'll prevent anyone claiming to you that 35C is sufficient.

Either you/they haven't put 55C into the system or, if you have, it is failing to deliver that. If the latter that's one for the installers/Vaillant I think.

I can say with certainty (and assumed I already had) that, as demonstrated by the calculations I gave you, unless you can get nearer to 55C you will struggle to heat the house with the current sized radiators.

Looks alright that!

You've got me thinking now @ProDave: a view through an IR camera would be interesting, and really help pinpoint the source(s) of the problem (and effectiveness of any attempted solution).

True, but they all have CPUs and some likely more in number/power than what the Heatmiser has (eg those with fancier displays, occupancy sensing etc) and yet don't suffer these issues. Agreed it's speculation though.

The best of both worlds is just to have a remote PSU. Thats what the ones with hubs do (the hub is the PSU) whilst others have a PSU local to the stat (but not inside). Some (eg Nest) allow either.

That said, many stats don't have slots in at all eg Nest and I think the Honeywell CM927 and Dt90 from memory. But then they don't have internal PSUs - I think *that's* the real design flaw. You should never create the very thing you're trying to measure.

I don't understand what you mean, but it doesn't matter. Just accept the figures. Again we answer; no - the heat loss from the pipe is negligible (resulting in a degree or two over a fairly long length if that) and even that which does occur is still heat into the house.

Thanks. So, with a calculated heating requirement of 3603 BTU that's 1056 W. Looking at the fairly common Stelrad Elite radiator tables, the output of a 600mm W x 700H Type 22 is 1207 W. However, that assumes an average ((flow - return / 2)) radiator temperature of 70C. With only 40C you are derating the output by 0.304 thus giving 366W so it will indeed struggle to heat the room. Furthermore, your heat loss calculator may only have factored in heat loss through the materials and not air changes thus the heat requirement will be much more than stated. TL;DR: the radiator is undersized for such a low flow temperature.

What type of radiator in reference to the following? And are the dimensions width x height?

Ah, yes. It's okay though I think - @Onoff volunteered to sort that out. ?

Truth be told I have actually 'left' a couple of times now but keep coming back. I can't help but feel we've all spent so much time and effort on this - and it really has been very hard work at times - that it'd be good to see it through to completion. Closure perhaps.

Didn't spot this line Zoot. Please show a little respect here. People are just offering suggestions - anything that might help you out - so don't complain about the order of advice given. There's no harm checking the basics have been done as with over 50(!) pages it's easy to lose track of what's been said. If you're not happy with our service ask for your money back.

Oh absolutely. I am just fearing 10 pages of getting everyone's hopes up.

Personally, if the tops of the radiators are as hot as the flow pipe I wouldn't expect there to be an air/bleeding issue.

Understood, and agreed, and I'm only thinking out loud (and not considering the inevitable differences the difference between how doable something is in theory vs practice!).

That doesn't necessarily rule out powering it via low voltage if the volt-free relay is powered from the low voltage side of the PSU.

Do I recall you saying the self-heating was suspected being down to the internal PSU? If so, could you remove that and just power it via low voltage from a remote supply?

Okay; I'll have to defer to others with ASHP knowledege/experience to see if that's normal. If it's going to work like that and never deliver water at 55C even when it is on it won't heat your house. Period.

I'll never forget once chatting to my plasterer and him telling me he can spot the 'fussy' customers because all their screw heads are oriented the same way. The look on my face must've indicated I didn't quite get what he was referring given the absurdity so he went over to the lightswitch to show me the types of screws he was talking about. Only when he got up close did he spot mine were perfectly aligned (horizontal of course; none of this vertical nonsense) then he checked the socket just in case it was coincidence. Oh no - I was one of *those* people.

Assuming the target set in the 'thermostat room' is high (please tell me you haven't left it at 15C or something) then - unless my ignorance of how ASHPs operate is showing - I would expect it to be running flat out whilst there's still a massive amount of heat required. With rads at 40C you're still only getting 1/3rd of what they would output at 70C. I know you'll never reach 70C with the ASHP but it's likely that's what the radiators have been sized for (if they've been sized at all). If you can get 55C from the ASHP you're only at 2/3rd max output - still below par but twice as much heat as you're currently getting. That'd surely make a difference to the rooms regardless what their construction is like. Personally I'd ignore the rads for a moment. Sit by the ASHP and measure its flow and return every few minutes. See how it behaves. If it's never going above 40C then *that's* your problem; not your house.

Okay good! I'd sit by the ASHP measuring its output - you'll see the changes soonest there and discover what it maxes out at. Then wander around the radiators doing their measurements. If the flow temperatures start dropping go back to the ASHP and make sure it's still outputting what it was.

Good and bad. Good because this is *exactly* why these measurements needed to be taken - you thought the radiators were hot but they are not. At least we now know you *do* have a problem and now know where to look. Bad because it is no wonder the rooms aren't heating up. Radiator temperatures of ~34C is simply insufficient if heat losses are high and the rads are 'conventionally' sized. You are getting approximately 1/5th of the radiator's output running at that temperature (based on the Delta T being 14C (34C - room temp of 20C) as opposed to 50C). The lockshields are likely too wide open too - too much flow. Don't worry about that just yet though - it's the ASHP that needs the focus. Were you able to measure the flow and return temps at the ASHP?