SimonD

You can design a system to cope with the low load, that's actually not a problem. The real problem I think is a methodological one. We design systems and size boiler from the outset at maximum required load, which we know does not suit the technology available because temperature and demand varies across the year - significantly and the technology available can't modulate for this demand. This means that we really need to look at alternative basic assumptions, one of which might be to design the system to the greatest window of function across the heating season -i.e. it is designed to modulate to at least 80% of heat demand window, with a recognition that it might struggle a little bit on the coldest if days and short-cycle on the warmest. However, realistically, if you installed max 12kW boilers where now we've got 18-30kW boilers going in they're going to modulate pretty well across the season. Then there is the problem of actually getting a boiler small enough. Try buying a 6-8kW gas boiler. The smallest I can get I think is a 12kW heat only unit. Then there's the combi situation, which is pretty dire because of the dual usage. In all these examples, you can see that none of the thinking is joined up to look at the problems systemically.

I'm aware the suggestion was about measuring gas consumption, but the point is that mean home heat demand across the UK is something like 6-8kW - how many boilers of that size actually get installed, if you can even buy one at that input. Efficiency loss from boiler short cycling is exponential rather than linear so the more short cycling, obviously the more waste. Assume an average loss of 6-9% but can be up to 11.8%. However, this is not all. With a poorly set up system - e.g poor radiator balancing, badly set up pump etc. - you can lose up to 30% efficiency in the system. Not only that, with frequent boiler cycling you also lose methane to the atmosphere through the ignition cycle. Your typical condensing gas boiler is about 89% efficient out of the box. It only becomes rated at 90-94% efficient depending on the controls fitted to the boiler. This is lab measured efficiency and assumed steady state. You've got to take care to set up a retrofit system to be this efficient on an ongoing basis, so 85% is optimistic for a typical installation that receives little attention.

Because they could be running a 40kW boiler that was slung in by some old school plumbing wizard that thinks they can size a boiler using their finger, a bit of spit and sticking it in the air - these are the ones complaining the most about heat loss calcs....probably. So the boiler is set to heat the house intermittently, without having any radiators balanced and it short cycles every 3 minutes. The customer is happy because the radiators are burning hot at 80C. All when the house only needs 8kW of heat input when it's -3 ..... Whilst in no way perfect, heat loss calcs actually do represent a leap forward in heat system design and installation in this country, believe it or not.

Try here: (Used to be JTM Plumbing) Good supply of all types of pipe insulation: https://www.plumbingsuperstore.co.uk/browse/pipe-insulation.html

This is where your difference lies as a glycol solution has less heat capacity than water (at 100% it's about 2500 J/kg K). Also, don't forget you'll need to add extra pumping resistance as a consequence of this.

Domestic Heating Design Guide I think you're slightly low on your figures. My calculation at Delta T 5 and 12kW equates to 0.67 kg/s mass flow rate which is about 40.20 l/m and 16l/m if your assumption of 40% distribution to the cylinder works out. So you're looking at a higher flow rate that you expected, I think. Formula taken from Domestic Heating Design Guide.

Maybe I've missed something but this calculation doesn't seem to include how much heat you're moving through the system, which is what you need to determine the flow rate in your heating system. What Delta T are you assuming? At what temperature are you heating your cylinders to? Your system currently works because I'd assume that your oil boiler was commissioned to work at a 70C flow with 50C return - so as an approximate difference, at Delta T 20 and a flow rate of 0.9m/s you'll move about 11kW in water, if you're running a heat pump at 7C Delta T this will move about 4kW. With glycol this will be less as you'll only move about 3,600J/kg K with 20% glycol content. Max velocity is usually considered to be 1.5m/s but more ideally around 1.

This is what they look like as used for fixing all the joists to the steels. No possibility of removing and then replacing the bolt as the whole fixing is the structural element. Thanks both, you've put me onto Rivnuts as an alternativ option but I'm struggling to find structural data for the rivnuts used for wider sections. This is something I briefly considered but followed the guidance of the SE and suggested fixings. I may just review this as an option. It's 3 meters drop so yes, I need to ensure it's robust enough. Currently the only option I know I can use is Interclamp/Kee Clamps tube clamp arrangements and depending on post diameter, I can install them up to 2m centres. Essentially what I want to do is come up with a design we like and then pass it by the SE as a final nod.

Thanks, yes makes sense. The bridge is made of steel box sections so bolts need to be hollo type which causes a bit of a headache. The longest I can find are max total fixing depth of 86mm so notching would be a must, plus they're so big, 33mm diameter hole is required through the posts. If I use Cedar, then stainless ones are over £100 a piece so 2k in total just for these ☹️ If I had my workshop, which is all in storage, I'd fabricate some brackets, which I think may be the only option but prices I've received to make them up also seem a bit ridiculous, but maybe I'm just tight? 😉

Yeah, me too - with some soft wet clay in parts that caved in without the digger being even close!

Well, I only have a little one 🙄 But of course it's how you use it that counts, isn't it?

Totally!

Or maybe it's been lying in the ditch for two weeks since?

(Expletive deleted) you're brave!

SW3.1 is the Dipswitch to enable 2 zones at equal flow temps IIRC. It needs to be set to on.

If you check the voltage at the top two wires where the terminals are label L & N on the FTC6, which is TB2, what do you get? You should see mains voltage there. Across S2 & S3 below you should see a variable DC voltage around about 20VDC.

So that looks very wrong! It looks like your LR from the UH8 is going to neutral on your FTC control board. I'm surprised there isn't a blown fuse somewhere. Have you checked the voltage you're getting at the Heat enable LS and then LR when it's calling for heat? Have you checked what wires are connected to your TBI.1 & TBI.2 terminal blocks? (bottom horizontal row of the FTC6)

Have you got a photo?

Have you got the correct fittings and jaw combo? Those connections look terrible, I wouldn't want them anywhere near an installation. Maybe better to hire a press fit kit, or even buy and then sell on? £1500 quid now is cheap compared to potentially fixing failed fittings later on down the road.

Sometimes it's not the one who's done the work. I've got so much criticism and scalding for redoing work that seems fine to others' eyes, not that I'm claiming to be a master builder by any stretch of the imagination, just want what I do to be right. But back on topic: Would a single T & G plywood subfloor replacement not suffice for replacement? That's what I would settle for if I didn't have the space for additional 6mm.

Try if you can to trace that cable back to the FTC6. I think these should go into TBI as that's where the inputs go, but these also depend on the DIP swtich settings. Although dealing with an earlier version, here is a thread I found that could be very helpful to read and it's about the same connections. I would also look at all your setting as even on weather comp. zones flow temps can be set to 60C I believe.

The Heamiser UH8 is a pretty dumb relay wiring centre so I would have a look at the wiring to the heat pump from the UH8 as per the following: Heat Enable This is the main call for heat for the system, there are 3 connections; LS = Live Supply E = Earth LR = Live Return Electrically this is a volt free switch, whatever supply is placed on the LS connection, is fed to the LR connection when there is a call for heat. Then check the wiring at the FTC6 controller. I wonder whether the 60C output is meant for DHW and the wiring centre is calling for that when it should be heating CH?

I would go with 6mm plywood, which is the normal spec for prepping floor for Vinyl, this even goes if laying on chipboard - usually recommended to be screwed down at 150mm x 150mm squares and 100mm centres along the edges. As for adhesive, she could just order some spray vinyl adhesive like this random link: https://www.best4flooring.co.uk/vinyl-spray-adhesive. Bostik also sell tubs of vinyl floor adhesive that might be a bit cheaper. Last time I paid for an installer to do a vinyl floor for me he even filled and sanded over the screws and joins between plywood sheets and achieved a very good finish.

Just approach a local timber merchant as they will almost always have machinery to both cut and machine profiles to your needs.

Here is a nice video showing and describing it very well. The towel rads could be run from the header next to the Esbe mixers.