marshian

Yeah the flow rate info and head is quite useful info - it's actual consumption is also handy I don't think it's actually as powerful as the old 15/50 so was expecting to have to run it a little faster speed wise ( I need to do a little experiment to confirm that) House does have two separate roomstats - one in the hall which if that ever gets to target it will turn off the boiler and one in the main living room which takes a fair while to get up to temp due to room dimensions and rad position (Long room - single rad at one end)

Useful comments I'll try to get my head round that - thank you Rad circuit is very well balanced (EB4 TRV bodies with flow restrictors so every rad pretty much gets the flow it needs at a sensible flow temp) Main flow and return is all 22mm copper with just 15mm copper tails from the flow and return to the rads (it's all lagged below the ground floor with decent foam lagging) no microbore or plastic anywhere. I'm pretty sure I know what to set the weather compensation curve up from a slope perspective the last few years I've managed to bring the previous boiler flow temp down from 80's to low 50's but any lower was pretty much a bust as min flow temp was 39 (38 was off) and even range rated to 10kW it's initial fire up was 75% of it's max (24kW) so it very quickly shot past the set point if less than 50 was tried The Viessmann system boilers are four pipe (I'm pretty sure) as well as not fitting inside a 300mm Kitchen wall cupboard - I didn't want the disruption of ripping up floors to run a second flow and return for the HW element of the boiler when a heat only with DHWP can do the same with a two pipe set up.

Sorry should have stated that DHWP was because I'd had the boiler set up with weather compensation - Long story but the Viessmann specialist didn't quite understand what I was asking for and didn't even know about the HW demand box that tells the boiler it's doing HW Currently S Plan with NC valve for HW and NC valve for CH (this one is being swapped out for NO valve to finish the set up properly) I'm reluctant to dump all the TRV's yet but if I find I can run without and just keep the EB4 Bodies which have internal flow limiters and put a decorators cap over them I will By Pass valve is a legacy of the old boiler which unless I had a little bit of flow thro it the boiler stalled in warm up and short cycled like crazy once the house was coming up to temp due to 4.5 kWh heat loss and 10 kW min boiler output was planning on having it set so it only opens when there is just one rad still calling for heat.......

Recently changed the house boiler From Flexicom 24HX (24kW with a 2.4 Modulation - ie 10 kW min) (Set up as Y plan) To Viessmann 100W 16 kW with a 5.0 Modulation - ie 3.2 kW min) (Currently set up as S Plan) Both are "heat only" boilers but the Viessmann (once the rest of the parts arrive) will be set up to run DHWP During the commisioning process the old Grundfos 15/50 pump speed lever sheared/failed and the pump was jammed on max speed. I was going to replace it with another one identical but it seems only refurbished ones are avaliable so as it's 20 years old and given excellent service I'd rather get something new. I've now replaced it with DAB Evosta3 which has three modes of operation Regulation with Proportional Differential Pressure (3 Speed or 6 Speeds) Regulation with Constant Differential Pressure (3 Speed) Regulation with constant curve (3 Speed) My brain can't cope with this level of options House has 13 rads all with TRV's and there is a ABV in the airing cupboard that will need adjusting once the autumn/winter/spring heating requirement kicks in I currently running it on pump speed 1 as I'm only using the boiler once a day for HW Any help in understanding what would work best

I'd definately do that..... I'd also be seeing if 1. Store temp was actually 52 or something much lower 2. What temp it was heating the store to on the legionaires cycle Quick on line math ignoring the COP of the heat pump from here https://www.omnicalculator.com/physics/water-heating Store temp 50 at start Store temp 60 at end Volume of water 300 L Energy required 3.5 kWh So 41.6 kWh is bonkers

That's a hefty wack of energy on a weekly basis I do a legionaires cycle once a week to coincide with Mrs BC's Friday bath - I heat the 114 litre tank to 60 deg instead of the normal 50 and the energy used is between 3.6 and 4.5 kWh depending on tank temp at the start. I heat it 1 hr before it's needed so the tank sits at 60 deg for that time I do have a vented system but have no concerns about storing water at 52 degrees - if Mrs BC didn't want a Friday bath I wuldn't bother to do a sterilising cycle - we use pretty much all the HW on a daily basis Some good articles here https://www.heatgeek.com/hot-water-temperature-scalding-and-legionella/

A couple of years ago it took me several months of every weekend to do the insulation retrofit install on my suspended ground floor. Working from the crawl space under the house (I had finished floors in most of the rooms that I was reluctant to rip up, ceramic tiled and oak boarding) but I have absolutely no regrets. It has had a bigger individual impact on energy reduction than double glazed windows, cavity wall or loft insulation did. I only wish I'd done it 33 years ago when we moved in to the house - I was younger, fitter and it would have hurt less!!!

I did very similar and I used treated tile batten to hold the PIR up (I did all my insulation from below the suspended floors as I have a 2-3 ft crawl space.

I have a steel pipe in the same configuration - well actually slightly worse - I have three legs on it 1. Boiler (1m Max) 2. Old gas fire removed and pipe capped (5m Max) 3. Kitchen hob (2.5m Max) It's been like that since the house was built in 1980 - Having a suspended floor and access to underneath I can confirm there has been negligible external corrosion over the past 40 plus years However I've never had boiler cover other than a manufactures warranty (same goes for any other electrical appliance where "extended cover" is available. I effectively self insure I divert a small sum every month to building society account to cover repairs/replacements for anything that breaks. As a result next week I'm replacing my boiler (which is 15 years old) before it fails - I'm not having to fund it on a credit card - it's a well researched choice (my current boiler was probably a poorly researched choice at the time) and is coming out of the "household fund" I've also previously done the same with pet insurance which is always a battle to keep to an affordable level as pets get older (although I recognise that this is probably a higher risk process) It's quite surprising how much people do pay on appliance cover - my neighbour does everything that way and he said his monthly cost was £260 - I put away £100 a month and it seems to work for me I may reduce that once I've paid the balance on the boiler replacement as it'll have a 10 year warranty but as it's going to be down to £550 (ish) I may keep it the same till it's built up above £1000 again

@JohnMo my thanks also for that handy tip - could not work out how to tag users - so simple now you've pointed out how to do it

Yep 100% - I think when the fitting was installed the scale built up around it and the rubber seal gradually degraded - leaving just the scale protecting stopping any potential water from getting thro - the combination of a degraded rubber seal on the back of the fitting sealing it to the tank wall and the gradual removal of the scale prompted the water leak.

We'd lived here 20 years and never had so much of a drop of water on the coldwater tank stand. The boards were soaked, as was the plasterboard beneath it and the loft insulation around it. I think we got lucky as we saw no tell tale marks on the ceiling - I just happened to be going up in the loft for the Xmas Decs.

Oh I missed this bit in your original post - we did exactly that (fitted a water softener) after seeing the scale in the tank It did exactly that - dissolved and removed scale in other parts of the system (in our case the cold water header tank in the loft (outlet fitting) and we had an unexpected surprise a year later)

There is a dilemma there for sure For me prevention is always better than cure - so I'd investigate the internals however I could - Drain down and remove outlet or inlet pipes and use one of those cheap plug in camera probes that work with a phone?

Several years ago I had to replace an immersion on a 118 litre vented copper cyl - the mount for the immersion had clearly been annealed over the life of the cyl and it started to twist and the copper was rucking up - continuing to try to remove the dead immersion heater would have resulted in fracture. It was easier to replace the whole tank so I did for one with an integral foam jacket (old one used to wear two puffer jackets) None of the metal reclamation yards near me would take the tank unless it was opened so I cut it open The level of scale in the tank as a result of moving it around was up to the top of the HW heating coil - the heating coil had maybe 10mm of scale around it. (We are in a hard water area) Explained why we frequently ran out of HW after a bath was run and why heating water used to have to be done at the same time as CH or would have to be done twice a day in the summer for an hour each time Fitting a new tank the water heated in 30 mins and could be done once a day and we haven't ever run out of HW on any day

Viessmann Heat Only 16kW with weather comp and DHWP I did consider the 11kW version but we heat only when needed rather than 24/7 so need a reasonable uplift in output to bring the house up to temp quickly Currently boiler can't do either - I did consider adding a volumiser but I was always going to have issues with short cycling

Very interesting - well documented - I'm not yet ready to go ASHP but I do need to replace the boiler because it's oversize 24kW for the house demand and the short cycle issues waste gas and annoy me even though I've range rated it down to 12kW. The new one will solve a lot of the short cycle issues but spring and autumn will be a challenge when heating required will be less than it's minimum We also prefer to cook with gas so going ASHP (with a grant means we lose that)

I've been data logging the house internal Temps and Humidity as well as the Loft (cold loft relatively well ventilated) Temps and Humidity for the last 10 months but I've spit the data into day/night (based on daylight hours as solar gain has a big impact on loft temps - south facing roof) I did this as I don't have MVHR and when I insulated under my suspended floors to reduce heat loss I saw a spike in humidity levels - I fitted a PIV unit to reduce humidity levels and I've been logging data since It's still not as low as I'd like but it's definately improved the feel of the house.

Very difficult to find the full specs of those atag boilers especially modulation or turndown ratios

We have a suspended ground floor with a sizeable void under it - I've insulated it and it made an absolutely massive difference to heat loss in the house - 4.3 was with an ACH of 0.5 - with default ACH it was around 6 from memory (this winter we were able to validate the 4.3 over a few days when it was around -2 for the whole period) Flow and return are 22mm with short 15mm tails to the rads and I have TRV4 bodies on the rads to adjust flow rates Viessmann 200 isn't suitable - won't fit the desired space - current boiler is 2 pipe flow and return at the top and I don't want to rip floors up to re-pipe for a 4 pipe set up - the difference between 1.8 and 3.2 isn't enough to convince me the upheaval required is justifiable Minimal change to the system required to go to a 100W heat only although the quote I got from the only Viessmann installer in a 50 mile radius is more than expected I'm still going that route. I tried setback with current boiler - it cost way more to run than scheduled heating times (almost certainly due to boiler min kW) I will try it again with Viessman when it's installed. I should add I'm installing with existing vented HW system due to not trusting 30 plus year old pipework with mains pressure I've already found 2 poor joints in the 30 years we've lived here and all the upstairs CH pipes run in the void between the floors and are quite tricky to get at.

I used this https://insulation4less.co.uk/products/tubolit-polyethylene-pipe-insulation-all-sizes I tried to get the OD of both 22mm and 15mm pipe insulation to be the same so I could set up the pipe lagger tool to work with both sizes so that I didn't have to constantly change the width of the cutting box

Looks like they've insulated flow and return together in one bundle - That was done in my house too - I've stripped it all off and insulated each pipe separately - made a massive difference to the return temps at the boiler as there was clearly some heat being lost from the flow to the return pipe driving down the delta at the boiler

If you can read a tape measure and know the construction of your house and the std/age of the double glazing you can do the heat loss calcs for a days work using https://heat-engineer.com/home for a one off fee of £12 I've done it myself early 80's 4 bed detached house (with some 90's insulation upgrades - SUDG, Improved Loft insulation etc) My heat loss at -2 came out at 4.3 kWh - current boiler is 24kW with a very poor modulation ratio (min 10kW) the heat loss explained why it cycles so much as even at -2 it's trying to push 2.5 times the heat required to maintain house temperature. We only have a few days a year at -2 most of the time it's 8-10 deg at which point it's trying to chuck 6 times the heat energy required to maintain the house temp. I've experimented over the winter with flow temps and with the current boiler I can get down to 45 - 48 deg flow temps - however this is mainly due to 10kW min input and a boiler min flow temp of 39 deg C and flow rate of 10L/Min I've also experimented with range rating the boiler to try to replicate what life would be like with a 11kW boiler and the warm up time is a little too long. The heat engineer software has told me exactly what each room needs to maintain a 20 deg room temp and I've been thro room by room sizing the replacement rads to run lower flow temps in preparation to a boiler change this year. (Viessmann 16kW - 100W heat only boiler which will be set up with DHWP and weather compensation - Yes I could go for the 11kW version but the min rating of all the 100W boilers is 3.2 kW so nothing lost by going for a little larger, we heat the house according to a schedule as we are at work during the day and slightly larger improves warm up time) So in summary 100% recommend a good heat loss survey Size your boiler (and rads) according to the way you heat your house and how quickly you want your water recovery to be - if heating constant (low and slow) you can size the boiler to be smaller - if heating according to a schedule you are going to want the boiler to be slightly oversize to get quick recovery of room temps

Ahhhh now that makes perfect sense - it did that once so I've set up my wiser so the "base" temp is only 7.5 deg. Unless a room reaches that temp when it's not scheduled for heating it won't fire the boiler and it's only the front entrance hall that's ever likely to hit that temp so for that TRV it's set to "off"

I know that - the question was directed to MrPotts as he's reverted to manual TRV's having had smart ones From my perspective a smart TRV does have a one advantage over a manual TRV - If a member of the household (I'm looking at Mrs Marshian here) turns it up because she thinks the room will warm up faster...... after 1 hr it reverts to it's previous set point (a Manual TRV stays there till I realise a. the room is too hot or b. I've burnt a lot more gas than normal)