larry

Hi, does anybody have any recommendations for a single room heat recovery unit? My mum has a well insulated small house, there is a 125mm hole in the wall already at fairly low level so ideally would need to be reasonably low profile, and reasonably quiet.

Good luck with it all!!

I'm pleased to update we've got through the first chunk of the first full winter with no problems whatsoever after the 'bypass cartridge' was replaced. We've had our first service also (boiler engineer completely perplexed he was coming out to such a new boiler but I want to maintain the 10 year warranty!). Working really well. And gas usage does seem somewhat down on our old baxi, though there are other factors also that will have contributed to that. V happy with the boiler set up now. Love the Viessmann app and the Drayton Wiser system that's controlling it is brilliant.

Hi sorry for a v slow reply - but no, we did not install a temperature sensor. Our boiler operation is therefore not weather compensated. In any case, I don't think we could utilise a temperature sensor for weather comp since our operation is controlled by the Drayton Wiser system (which just turns on/off)

It absolutely is, isn't it? It really strikes me that in the same way that we have all become mini epidemiologists in the last 18 months we now need to become mini building scientists. Everybody needs to take an interest in their house and understand roughly how it was built and what that means, particularly anybody living in an older place . This knowledge needs to be taught in schools. And builders also need so much more of this information. It's a huge task for government and it feels like the sense of urgency is just missing. Anyway, I go on... We are retrofitting (1920s with solid walls) but doing it slowly, room by room, so we can still live in it. As I say, huge amounts of learning and so surprised at how much you have to dig to get answers to questions and problems which many people must also have had to ask/answer.

Blimey Simon you are a wizard. You clearly know your onions here. If you fancy writing a 'shoulds and should nots' list for people facing the task of IWI I'm sure a lot of people would benefit. Theres a lot of (at least apparently) conflicting info out there for us DIY but do our bit to save the world types. I've now finished my second room, they were the easy ones! Learnt a lot though already....

I've used a scraper with a Tungsten Carbide blade recently, screwfix had one for about £9 and it has been absolutely incredible, though more for gloss than walls. Buy a few spare blades if you're doing a large area though Your logic all seems sound to me but I am definitely not commenting from a position of expertise. What sort of plaster is it? If gypsum skim then I guess quite likely to have a PVA coating underneath which will not be breathable even if you strip the paint off.

Hello Seeking advice on this issue! We have a chimney in the middle of our house, currently unused and I don't think ever will be. There are three flues, two to old fireplaces in bedrooms, and one to an old fireplace in the kitchen which has been removed. We have had some pigeons fall down the chimney which is obviously lovely in terms of resultant effects... I have spoken to a roofer about coming to cap off the chimney, but I wonder if I should ask them to be doing anything else at the same time. How worried to I need to be about maintaining ventilation (given it's in the middle of the house, not on an external wall)? Am keen to improve insulation where I can also. There is another option to remove the top of the chimney stack to roof level, though can't quite work out whether there are other benefits of that other than not having a chimney stack to maintain. THank you all

Ps, yes nick, bypass valve was replaced (twice!). And it wasn't just dumping heat to the rads after a call for DHW but from the very moment a call for DHW started.

I'm as perplexed as you are Mark, but the boiler remains in continuous operation mode. The setting "switch off in reduced mode" is turned on (and has been since install). Viessmann (not valliant) advised that this was the right mode for our setup, this from the central technical team as well as both technicians who visited and the installer. I realise it doesn't make sense but it seems that continuous operation mode on this boiler does not mean what it says on the tin, at least if the "switch off in reduced mode" setting is on. The problem was present prior to the most recent visit by viessmann, they have changed the bypass cartridge and the problem no longer appears to be present. If that's helpful for anybody struggling with a viessmann 200 where it looks like a diverter valve problem but isn't, I'd be delighted. I promise I'll update if things change either with the fault recurring or when we get to weather that needs regular heating!

Haha, fair point Though we've got weather comp off and when I put the Drayton Wiser system onto 'boost' the heating kicks in as I'd expect. But yes, fair enough - I'll update in November!!

OK - well it's only been a day, but I'm also saying this seems to be fixed. I can turn the hot tap on and the heating pipes no longer start getting hot immediately. And, even on minimum burner output, the boiler fires up, makes the water hot, and then turns off again. Mark I have to say I'm not 100% sure I completely understand what you're saying, but if the rads now get hot when they should do and the DHW now gets hot when it should do, and it doesn't seem to be doing anything it shouldn't be doing, what's the problem? It's working just like our previous combi boiler was working? Nick, I suspect my patience might have been thinner if this was January I have to say I was generally impressed with Veissmann. OK, so it took just a little while for them to figure out the problem (!) but there was no issue in getting them to come out whenever I called up and the engineer did seem to invest a lot of effort to sort things out.

This is hopefully (!) the final update on this thread... we have had a couple more callouts and the engineer has replaced the 'bypass cartridge'. He sounded very confident that this would be it so I have fingers and toes crossed that he's right. I'll update again if the problem re-occurs

And this one: https://strawbalebuildinguk.com/wp-content/uploads/2017/09/breathability.pdf

Thank you so much again for coming back to this, this is a mine of information and hugely helpful. I loved the " you can't argue with water as anyone who has been to the grand canyon knows" quote, I'll remember that one!! (I haven't, by the way!) I've actually done hours (days) of reading around this - though ultimately I end up feeling like I'm chasing my tail with this - I'm not a tradesperson but have a sciency mind and always like to understand things for myself hence why I appreciate your reply all the more. Some of the things you'd flagged I'd already 'worked through' in my mind. The cement render on the outside has been there a long time, it's possibly ? original but I'm fairly certain cement not lime (Youtube suggested pouring vinegar over a small section to see how much it fizzed, and the lime plaster was much fizzier!). But obviously somebody has added the extra layers to the internal wall more recently. We've fitted an MVHR system already - and yes I can see the multiple arguments to and fro doing this in an old house, but already we notice improvements in air quality even if it isn't doing loads for 'heat recovery', and as we're doing a lot of work with access to floorboards and ceilings it felt like the right time to do it. So that may hopefully help with the ventilation side. In terms of the 'is gypsum breathable' or 'is plasterboard breathable' question, you are clear that it is not, but the reason I am so confused about this is because I have read people stating this (agreeing with you) but also the opposite in equal extremes: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9580 https://www.engineeringtoolbox.com/vapour-resistance-d_1807.html https://www1.eere.energy.gov/buildings/publications/pdfs/building_america/building_materials_property_table.pdf https://www.greenbuildingadvisor.com/question/gypsum-board-vapor-permeable-or-what ("very permeable") This must be an issue of fact, surely? Or there must be other elements of the equation that I am missing? In any case, the Mike wye plasterboard definitely looks something to look into - I haven't seen that so thank you for sharing/suggesting that link

I should add, the wall (outside in) is cement render, solid brick, lime plaster, paint X 2 layers, gypsum plaster skim, lining paper, two more layers of paint... Which might account for water getting trapped behind I guess?? I'm painfully stripping it back to the lime plaster layer then putting the wood fibre on top of that. Got to be more breathable than before??! Also, same question about the plasterboard... Not breathable??

Thanks so much for such a helpful reply. Though I'm a little confused, I have read elsewhere on this forum that gypsum based plaster is just as breathable (vapour permeable??) as lime plaster, it's just the stuff like PVA that people add which causes the problem. I am not claiming this as fact ( way beyond my expertise) but is this incorrect or a misunderstanding on my part? If so presumably I could patch with gypsum based plaster, no PVA etc, and let the wall breathe away? Or do snares lie in that direction also?! Thanks again for your advice and expertise, I do appreciate it!

That's a good point about chasing... Hadn't thought of that!!

Thanks so much JFB. That's hugely helpful. It's the second room that we were doing. For the first we had Pavatex Isolair, recommended by Mike Wye, and fixed that directly with the plastic plugs and then a lime plaster system on the top. Was keen to try the other method for this room partly to learn a bit more myself but also partly as the 'headline' price of the Steico Flex was significantly less than the Isolair or similar rigid boards. It also allows a gap for a service duct behind the plasterboard so I can run cables for a new ring, which is very handy. Over time we do plan to do the whole house so I'm treating these first two rooms as a practical classroom!! Thanks again, appreciated

Hi, We are slowly working around our house doing IWI using Wood Fibre insulation. In our upstairs bedroom (3 external walls) I am using 80mm Steico Flex, in between wooden studs, with a plan to then counter batten and plasterboard on top. In preparing the room I've come up to an upstairs external corner where there was a very old cast iron pipe buried in the wall, presumably supplying an old radiator - it goes about 2/3 the way up the wall. As I pulled it off of course a lot of surrounding plaster has come off and I've got a nice section - perhaps 1 sq m - back to brickwork. It looks like the pipe acted as a point for condensation since the area immediately around it is buzzing on a damp meter somewhat more crazily than the wider area around it. Though those have been reducing over the last few days so presumably it is now drying out. Do I: a. try and reinstate the plaster prior to putting on the same thickness wood fibre insulation so all the plaster is level (and if so with what? I've got a bag of gypsum browning plaster to use up....) b. get some 100mm wood fibre insulation for the 'back to brick' section so the area is roughly level with the rest c. pull all the plaster off the whole wall and then apply the wood fibre directly to the brick d. do something else And, to help my learning - why?! Wall is solid brick wall with external (cement??) render outside. The original plaster had had a skim layer on top, and then papered and painted. I've managed to scrape off most of the skim plaster so it is otherwise back to the original lime plaster. No obvious evidence of a damp problem historically or in the time we've been here (5 years, it's a 100 year old house) Thank you all

Hi Mark, thank you so much for these replies. Your first post particularly I think really helps me get my head around what the boiler likely thinks is happening here in regards to trying to keep the plate exchanger up to temperature but failing. I do think the engineer who has visited as tried to rule out the first three options, certainly new diverter valve, and replaced logic boards. He's also I think said he's tested the switch etc. In regards to the 'continuous operation' mode, this was exactly what was advised by Veissmann. I was completely surprised also. I think it is essentially 'not weather comp' mode. The service engineer who has visited has recommissioned the boiler (several times) and kept it in this mode. It has a 'switch off in reduced mode' function, which turns the pump off when there is no call for heat, and seems to essentially be to keep the flow temp to 20'c when there is no call for heat/DHW. In terms of a diagram, it's a pretty simple setup. Two main 22mm pipes with 15mm branches. The 22mm pipes drop downstairs to feed most of the rads downstairs except one, which is on a separate 15mm drop (concrete floor). No pumps. About 16 rads in total, reasonably large detached house. Engineer opined there might be a 'short circuit' somewhere in the pipework or some kind of crossover - Whilst I suspect some of the rads are the 'wrong way around' I don't think there's more than this as I've seen the majority of the CH pipework under floors/above ceilings etc but my next plan is to turn all rads off from the lockshields and see what happens. If that fixes it, then to open the rads one by one. Ultimately, it's a 3 month old installation with a '15 year guarantee' so this really should just be for Veissmann and the installatio company to sort out, but I want to be a helpful customer!!

OK, so I promised an update. Viessmann engineer has visited today again. He has replaced the hydraulic block. He has also replaced both control boards on the boiler. Probably spent about 4 hours with the thing. The poor chap. Seemed to be working when he left but.... no dice. As soon as I turn the 'minimum burner' setting to 10% then the burner will not switch off when there is a call for DHW. With the setting above 10%, then the burner will turn off and it appears to operate properly. However, in all cases, whilst there is a call for DHW the boiler is dumping hot water to the heating circuit (not just afterwards, but whilst the tap is running). So, basically he's fitted us pretty much almost a whole new boiler and we still have the same problem. So, my logic is it can only be a 'settings' issue or a 'system' issue. The fact that the boiler worked fine for 8 weeks or so and the problem appeared out of the blue seems a bit mysterious. The fact that our previous installation worked fine with our old Baxi combi boiler and this just just been fitted to the same pipework seems to point against a system issue? Interestingly, the Viessmann engineer tells me that when the heating circuit is fully closed off the boiler seems to behave itself. So... not quite sure where to go next, other than back to the installation company again. Might try isolating the rads one at a time to see if that makes a difference.... though I really can't be bothered! I will post in here and updates and any smart ideas are welcomed. So... going back to the original question: would I buy the boiler again now? No. Not really.

Next update. Viessmann engineer has visited again and replaced faulty diverter valve. It made no difference, so that's not it! Lots of head scratching. He's now going to replace the 'hydraulic block' (I may be using the wrong words, it was definitely a 'block' of sorts!) which apparently he has never had to do before. In the meantime, I have fiddled with the settings a little and found that I partly solved it through increasing the 'minimum burner output' setting, up to about 15% from 5% previously. However, the boiler still seems to be dumping hot water to the radiators whilst there is a call for DHW and no call for heat. And, of course, my main reason for buying the boiler was because of the ability to modulate output magnificently, which of course this then obviates somewhat. Engineer visiting again this week. We'll see what happens. And I'll update on here.

Good to see somebody else using the Sikaflex EBT stuff!!

I've been doing ours. Have had success with using cement covered EPS panels - e.g. https://www.wickes.co.uk/STS-Professional-Tile-Backer-Board-1200-x-600-x-10mm/p/101131?utm_source=google&utm_medium=cpc&adpos=&scid=scplp101131&sc_intid=101131&gclid=CjwKCAjwhYOFBhBkEiwASF3KGcxP17L0HyFemITNRpCmxbXYJw2LAyzE5dHU4DwsrW68PoWuimnRjhoCb6UQAvD_BwE&gclsrc=aw.ds Currently at £9 from wickes per 1200x600 board which is reasonable I think? Found a pre-made niche on Ebay, but would have been happy cutting the above board (cuts easily with a utility knife) then gluing it with Sikaflex EBT (which is fast becoming my new best friend, particularly when it goes down to £5 a tube) and then putting waterproofing/tanking tape - e.g. this https://www.tilefixdirect.com/product/Orbry-Waterproofing-Tape?gclid=CjwKCAjwhYOFBhBkEiwASF3KGR6ONX4n2EYwVVpVoHCRbAM4OT3jhc5VB6AXYvdbeS4mgflMjk52hhoC5VcQAvD_BwE over the gaps and joints. Then using a good waterproof tile adhesive before tiling. Most of mine is onto a stud wall, and had fixed PB to the wall before putting the cement facing boards on top as I just wasn't quite convinced about rigidity of the board. With the tiles, grout, tile adhesive, tanking tape, waterproof board I reckon it should do a pretty good job keeping the water back. Completely DIY so I have no doubt there's a better way but have tried this approach now in two bathrooms and seems to work well Good luck with yours!