marshian

to round this slight off topic element off - london loop fitted to return from coil - was a right pain to make and fit because of space constraints in the airing cupboard but I normally see 0.66 deg tank loss per hour (it used to be 1 deg per hour before I reconfigured the zone valves) 1900 hrs yesterday - heated the tank to 50 deg - at 8am this morning it had dropped to 46 deg (no major consumption of HW during that time) 0.3 deg loss per hour is an improvement The biggest obvious sign was that flow and return pipes at the boiler were identical - normally I see a higher return pipe temp before I even start space heating I don’t need one on the top of the coil because the zone valve is right next to the coil inlet. I might have to put one on the HW tank outlet now as that’s probably another driver for the losses.

Some spark plugs are 17mm so it shouldn’t be hard to find a box spanner or a spark plug socket - they are extended length

Oh and below is the response from Viessmann technical regarding range rating the boiler (I have another email confirming the same for flow temp max, also adjustable for CH only (not when using HWD box)

Thank you @JohnMo I only really notice the “leaching” when I’ve done the weekly legionaires cycle (an hour or two before some HW is consumed) and when I heat the water much earlier than I need it (like at a weekend when it could be a couple of hours before any water is used) The return side of the cylinder is a bit horrible right now so I’d like to tidy it up and this would be the ideal time to stick a london loop in - even if it has only a small benefit window I might as well put one in

Slighly off topic @JohnMo because I can’t find the thread in question when installing a london loop - does it matter if you have to go up 15cm to then go horizontally for min 15 cm then down for 15cm, across horizontally for 15cm and then up for 15cm? I can’t fit a london loop on my HW tank return without doing this as I’d have to go down into the floor and through a floor joist - if I go up first I can package a london loop easier - it won’t look pretty but it can be done

I asked Viessmann technical help if I could 1. set the max flow temp lower for HW (when demand box was being used) their response was no - it’s preset to max flow temp 2. Use the max output setting on the boiler (range rate effectively) to reduce the kW being used when doing HW (using the demand box) their response was no - this would only impact the CH side the demand box calls for max boiler output and only modulates down when the return temps mean it has too. As a result I shall do what I said I would do earlier in the thread and in none heating months switch back to dumb boiler mode. I will say it’s reheat time is bloody fast - this morning tank was 20 deg C (we’d used all the water yesterday - bath night) and in 18 mins it was 54 deg - I don’t need that speed in the summer 🙂

Because DHWP maximises efficiency on CH but sacrifices a small amount of efficiency when heating HW So when you are using CH the gains on CH running weather comp flow temps out weigh the drop in efficiency when doing HW In the summer you have no need to use CH so I can revert the boiler to non DHWP and run the flow temp at 55 deg C - the boiler runs for 1 hour to get the tank from 25 to 45 (maybe 48 max) it's in condensing mode all the time and the gas usage is lower compared to DHWP when the boiler throws everything at the HW circuit in order to minimise the time spent doing HW and get back to CH asap I've had the opportunity to run the boiler in both modes and I'm pretty sure my data doesn't lie to me. How do you run a heat pump to get the best SCOP or COP - low and slow WC is all about minimising boiler flow temps - keeping the boiler in condensing mode maximises efficiency but to do that and not lose heat in the house you want min down time from heating hence DHWP DMHP for water is actually the exact opposite - chucking everything the boiler has at the HW circuit is not low and slow and there is energy lost to the Flue - why would I want to continue that wasted energy thro the non heating months?

100-W heat only is two pipe - it doesn’t go down as low as the 200 (min 3.2 kW) I’m using a std vented 115 litre copper cylinder (50 mm foam coated) with basic tank stat so doesn’t have the largest heating coil in it (maybe 3kW max) The boiler does modulate down as the return temps get closer to flow but start of cycle it throws everything it has kW wise (rated at 16kW but my readings from the gas meter over a short period of time says everything is just shy of 21 kW 😉 In summer in the installation settings I’ll just switch the boiler back to dumb (B5 then C7 and then select 13 rather than 4 and it’s back to a normal boiler with full control of the flow temps, no weather compensation and no HW demand function) so in a nutshell no wiring changes

I have Viessmann 100W "Heat Only" 16 kW with HW demand box and WC It will raise the tank temp from 25 deg C to 50 Deg C in 15-18 mins with a std vented Cylinder Coil In autumn,winter and spring I will run the boiler with DHWP - I want it done in as short a time possible so boiler gets back to CH running weather compensation at low flow temps Summer when I'm only running HW I will revert to heating HW low and slow as there is a small reduction in gas consumption compared to DHWP when the boiler hits the HW as hard as it can Next year I will look to replace the current HW tank for one with a bigger coil (it should shorten the time for HW in any season but enable the boiler to condense better in summer with a lower flow temp) I will experiment with range rating the boiler because I can't lower the flow temp of the boiler (80 deg C) when it's heating HW - it maybe I can't lower the output either but I'll find out soon enough

Well time to round this out (Not quite there but damn close) No mater what I did with the Wiser Hub (controller) - All Off, HW On, HW Off, CH On, CH Off or Both CH and HW On the wire from the wiser unit to the wiring centre to trigger the HW was live all the time. I was completely confused by this as it shouldn't be live unless the timer is calling for HW but I checked the wiring instructions and it was all wired correctly 3 for HW and 4 for CH I swapped to a different (spare wire) - same result 240V all the time unless the power to everything was killed The CH wire is only live when the timer and the room stat is calling for heat Every time I check wiring in the wiring centre or remove the Wiser Hub I switch off the power to it all at the Fused Spur that feeds it all I don't know why I did what I did next but I took the Wiser hub off the universal back plate without powering down and I heard an audible click and I stopped - a penny (very large one dropped) - selecting CH or HW had always made an audible click but since the boiler install and change of wiring that had been missing for HW the light comes on but no audible click. I switched off the fused spur - re-attached the Wiser hub and if I selected HW I got a audible click, CH again I got an audible click Going up to the wiring centre with nothing selected on the hub I had no power to either HW or CH signal wires Selecting HW gave me 240 volts and same with CH with nothing selected I got no Volts on either HW or CH My only thought is that somehow the relay or contactor for HW had stuck closed and even powering down the unit was not causing it it open. Anyway everything now works and just need the gas engineer to confirm with Viessmann that a switched live back to the boiler is needed (I'm damn sure it is but I'm not about to fit that) I actually need to think about how the boiler gets that in summer or if heating water outside of the CH period because I can't have both CH and HW linked to the same switched live signal to the boiler or CH will drive HW I might have to either A. think about a relay solution or B. think about a switch (Summer / Winter setting) I can only have one SL wire at the boiler so for Summer the SL comes from the HW side but for winter when I only heat water during the CH timed period it can come from the CH side.

And there is my problem - I got the only Viessmann trained gas engineer for 50 mile radius to do the job - the other installer 50 miles away didn't want to quote because the distance made it not worth his while................. Maybe I should ask Adam from heat geek if he fancies a boiler challenge............

Sorry had to rip apart my bath room to replace a shower waste that was letting in smells So connected (Not me) but AFAIK Outside temp sensor yes HW Demand box Power to the Boiler (Live, Neutral and Earth) After that sorry but not a clue

Just to round the calibration element of the thread - I’ve had both sensors over a NaCl slushie for a couple of days at room temp one required an adjustment of 2.7 and the other 4.5 (both cases they were over reading) so I’m a smidge less concerned about my humidity levels now thank you @Sparrowhawk

Sorry for slow reply - my attention has been diverted to bathroom issues shower waste needed replacing and access was too tight with the soil pipe in the way - luckily I did the bathroom myself so knew how it all went together Later today I’ll check out the boiler connections

as the link is external to the PCB I decided to remove it……. No pump at all

Highly likely - That will be down to the gas engineer to resolve - I'm absolutely fine with doing everything outside the boiler - not so fine with stuff inside it.................

Whoa @JohnMo That link has this diagram - It's not in any of the documentation I got with the boiler or HWD box or weather sensor........... Is a W Plan similar to X plan with a 3 wire NO CH Valve??

I’m trying very hard to do three things 1. understand how it works 2. Save the life of a fuse by not getting it wrong 3. Keep the smoke inside the wires thank you for your input but this is not my strong suit so I will be painfully slow in progress

What connection?? boiler has Direct control of the pump HWD box wired in Weather Compensation sensor wired in The boiler has been “told” to run in weather compensated operation mode The link wire is still in place and I think it’s running on a permenant live and Neutral only with no switched live in sight But as I’ve said electrickery is not my strong point - if it’s got oil or water in it or it needs to fabricated in steel or wood or whatever I’m fine with it

it’s connected and it sort of works - just haven’t documented that section of the wiring on my schematic sort of works………. I currently have to turn the boiler off to stop CH - it leaves the pump on 24/7 even if the controller says all good house up to temp lets wait for the call for more heat flow temp of 32 deg C today and all rooms are at target temp on trv’s so all the flow is going thro the bypass right now so I’ve stopped the boiler in the ViCare app

Current state of wiring centre orange now located in bottom right and linked to HWD box grey is now in the live lot (top row left side) Reminds me - all the grey cables at the bottom were clamped before the install after none were clamped and the clamps were gone….. as a result I bought another L16 wiring centre to get new clamps and screws because I was less than happy about unclamped wires in a traffic area (SWMBO) keeps her ironing board and irons on the floor and shes a bit heavy handed Remember this is a Viessmann trained installer - only one in 50 mile radius I hate ending posts negatively - shat’s done is done I’ve clearly reached a point where I need to do this myself and any help or advice in this direction is appreciated and I can move forward positively

Just to repeat - I asked for X plan - I got S plan (2 NC zone valves) with weather compensation (turned off because I like HW not CW) and set it up with a 55 deg flow temp no HWD box no wifi interface (was on back order) Installer came back with one new NO zone valve, HWD box (after I told him the part numbers for both) and said will you order it or shall I?) and the long awaited for wifi module he’s had two opportunities to get it working right on x plan DHWP and hasn’t really got it right - I still have issues with control on CH side so I revert to what I often have to do “If I want a job doing properly I need to do it myself’ DIY means starting from scratch working out what all the wires do and drawing up a schematic that makes sense to me - Electrics are not my strong point but so far no fuses have been sacrificed to my electrickery knowledge quest

you’re a very clever chap but either I am really rubbish at explaining stuff (and I can accept that criticism if I am) or your reading and comprehension skills are a bit poor and I’m going to assume it’s the former rather than the later for now As I said in earlier post CH side is not fnished in the drawing - I’ve just managed to get the HW side working as it should along with the transfer from CH to HW and back to CH having completed HW - not finished would account for some missing wires OK

You do realise "my drawing" is of all the wiring centre (well when I finish it) and what you have posted is a diagram of how the HW demand box integrates with the boiler 😞 I must admit I've borrowed the base drawing from an S plan which is what the gas engineer set the system up to work as despite being asked to set it up as X plan!!! 51011_01-mBox-L32-S-Plan-connection-drawing-FRAMELESS.pdf

I must have watched that video a bunch of times and I've not spotted that element Annoyingly the only video that Syzmon has done that featured a Viessmann 100-W B1GA turned into a little whinge fest about how he wasn't impressed about the fact the HW demand box and wifi module were add on units and the boiler front cover didn't have a sound insulation panel in it like the system or combi boilers did. He was making a valid points The HW demand box is a bit of an add on The Wifi module is hard to fit in the space and route nicely - if the ribbon cable was 2 cm longer it could be routed away from everything and look much neater than crossing the PCB at 45 deg When heating HW at 100% modulation the 16kW rated boiler I have is throwing 19kW and 80 deg flow temp at the HW circuit and it's nowhere near as quiet as it is when it's doing CH at 3.2 kW and 37 deg C I didn't want to convert to a 4 pipe system for all the disruption that caused and I wanted a boiler I could hide in a 300mm dept cupboard because SWIMBO wants to change the kitchen from white to black/dark gray and a white boiler on show would look crap Sometimes we have to compromise to someone else's needs/wants