FlatMax

I think this is good advice so I will have a round up once we get into the warmer weather. Your usage figures for Saturday 20th December are like chalk and cheese compared to mine! Admittedly, our house is large at 340sqm (and 1,120cm volume) and It was a warm day for us here in South Devon. Even so, I used 45kWh for just four hours of scheduled heating in the morning whereas you used c55kWh for the whole day. The take-home message from your post is that I need to explore more fully load/weather compensation controls that can be used with the WB, so that its turndown output of 3kw can be more efficiently used. The problem as I see it (looking at the reviews in December 2025), is that all the weather compensation controls are somewhat unreliable, especially so the WB Easycontrol. I need a truly bomb-proof fit and forget system; at the moment I'm not seeing this in the trade reviews.

Thanks everyone; most helpful. So, @JohnMo I have re-rated the heat loss as per the scale shown by @marshian; it's Category three, pre-2006 new build. Using this chart gives 30-50w/m2 so between 10.5kw and 17kw plus 10% for on/off. If I take the mid-point then it's 15kw including the 10%, so I am too low at 12.5kw as @JohnMo says; I'm going to range rate it for 17kw and see what we get. Just as an aside, how quickly should the rads heat up to 50C if the boiler is correctly rated? Ours are taking about 45 minutes. (BTW @SteamyTea, there was no call for DHW when the CH was running) I'll post an update, but again many thanks for taking the time to respond to my query. Cheers.

**UPDATE** Following all the great advice kindly offered on here, I managed to establish a working relationship with a WB approved installer just a couple of miles away. The ageing Baxi 105e has been replaced with a WB Greenstar 4000 rated at 30kw for DHW/24kw for CH. I calculated the heat loss for the building at 12.5-15kw (it's a 2002 build of 340m2 set over three floors, with total volume of 1,120m3) at ambient of 5C and inside at 16C. We don't like the house too warm, so these metrics are fine for us. The boiler has a turndown ratio of 1-8, so 3kw up to 24kw is the operational output range. Before looking at weather compensation, I've been experimenting with simple inputs like range reduction, flow temperatures, and proper use of our existing TRVs; the system remains under the control of a Hive Mini on/off arrangement. The original twenty radiators were substantially over-sized when the house was built in 2002, so this will work in our favour for a 'long and low' regime. I've range rated the boiler down to 50% (12.5kw) and reduced the CH flow temp to 50C; I have also dropped the DHW to the same value and might go lower than this eventually. All the rads were balanced with the TRVs wide open and heat loss across the panel is around 10C. All the rads across the three floors heat up fairly evenly from cold, and after two hours the house is really very comfortable. The boiler's return temperature after two hours of heating is 44C and it's condensing really well; the amount of water it discharges is extraordinary. Now the fun bit for the techies on here. Having range rated the maximum CH output to 12.5kw, how come my Octopus smart meter says I'm using 20kw per hour of gas when the boiler is firing from cold? The half hourly plot does show the boiler modulating down a bit as the system heats up, but it's still using around 18kw each hour. The input to output ratio for the boiler is almost the same, so I am completely mystified. Am I wrong in believing that 12.5kw is the most the boiler can consume for CH?

Thanks to everyone who has been kind enough to post their replies. I think I now have all the info required to make an informed choice. What I really need to do is find an installer with whom a reliable relationship can be established; we don't have that at the moment.

I hadn't even considered this; thanks for the insight. Here in South Devon we don't get much below 10 celsius ambient during the coldest months, so I can keep the house at 20C with a flow temp of 55C no problem. We have twenty rads in total (thirty five panels if you count the double rads) spread over three floors and 2,500 sq ft floor area. Building was new in 2003, so half decent insulation. What would you consider is a good turndown ratio for a modern condensing combi? Our old Baxi has a ratio of 3:1 which oddly, is the same as the latest Duo Tec 28! Thanks again.

Hi everybody. Our 2002 Baxi 105e instant has been (and still is) a cracking good boiler, but of late it is becoming increasingly unreliable with niggly random issues mainly around control items. I've done numerous jobs on the water set over the years, including swapping out the PCB, thermistors, and other bits which are still readily available just about anywhere. The latest iteration of what can be described as 'random' faulting, is that the boiler locks out when you shower whilst the system is calling for heat; you are then left with the flashing 50C LED and DHW symbol, and the pump running continuously. Powering off for half an hour and reconnecting sees the boiler run its usual ignition check and hey presto, all back to normal! Central heating functions as normal, and DHW as well, just not both together. I'm guessing the overheating is something to do with the diverter valve (the DHW diaphram is new) but my wife has pointed out that the boiler is probably at the end of its service life, is less efficient and more polluting than a replacement, and she would be stuck if I wasn't around when these things happen. All this is very true, so I'm looking for a replacement. The Baxi Duo Tec 28 is the replacement I'd go for, as it sits on the same jig and has the same pipework/flue configuration. I'm not looking for big efficiency savings here, just another boiler that will last 15-20 years and be more reliable going forward. Parts are also readily available for this model and it has a seven year manufacturing warranty. Do members think this is a good combi boiler or are there others out there that are significantly better? Any advice would be gratefully received.

So to conclude, the fault lay with the incoming leg of the ring that descends down the damp pier into socket 6. As #AndyScotland hinted, the cable is bent at a 90 degree angle as it enters the wall so somewhere in the two metre drop to the socket, the twin and earth has degraded over the years. I'm going to cut and terminate that leg of the ring into a safe socket until it can be disconnected at the MCB. The other leg of the ring will now be a radial protected by a 20a MCB retaining the original six sockets. Before finishing, I just wanted member's views on regulatory compliance. I am perfectly capable of replacing the existing MCBs and single RCD with six RCBOs, but believe this is what is regarded as 'notifiable' work. As I am not a registered sparky will I need to get one to test the residual current of each RCBO and sign off the mods? Is this correct, as BS7671:2018 is not statute law, just guidelines for safe systems of design and working? An electrician has been in touch at last and I'm tempted to just give hime the job and have done with it. Anyway, thanks again to everyone who has commented and contributed; it's been a big help.

You are right. The part of the lower ground floor where the issue lies used to be the underground garage of the old house, now converted to a habitable room. We don't have water running down the walls or anything, but the pier where the socket is set has always been damp. I am looking into fixing this once and for all with a local damp-proofing outfit.

Thanks ever so much everyone; really helpful response. I cleaned the corroded cable ends (that is the end outside the plastic) back to copper using dilute hydrochloric acid and rinsing/drying. It looks like corrosion has crept up the CPC right into the flat sheathing. Assuming that's the same for the phase and neutral (and that it's very damp as well), will that be enough to allow current to leak past the plastic insulation surrounding the copper core? I have blown through the conduit between box 5 and the suspect box 6, and there is no water pooling inside. The earth leakage clamp test was done with all the board energised; I thought that would indicate if there was any significant loss elsewhere. The maximum load likely to be taken from any appliance in this particular room will never exceed 7 amps, so a 20A RCBO/MCB will be fine if I decide to convert to a radial as suggested by #FuerteStu. I'll start by isolating the run between the suspect socket 6 and socket 5; if it holds then I guess I'll be ordering a 20A MCB. (Just as an aside, I did put 12v DC down the ring and got no voltage drop whatsoever, but I'm guessing this would not be enough voltage to expose any fault. I think a Megger uses 500v DC or something?) Anyway, thanks again for the very positive and constructive suggestions; I'll post the progress (or not, as the case might be).

Hi everyone. My query involves a ring final circuit in our lower ground floor. The house was built in 2003 so is 16th Edition regs. The CU is a Hager split unit with six 32A MCBs with a 30mA RCD, and six 6A MCBs with the isolator switch to the far right of the box. The room has six twin sockets and as far as I am aware none are spurs; they all run around the perimeter of the room and I can identify where the ring enters/leaves the room. There have been no alterations to any sockets in the room since new. Last week the RCD tripped the whole house and by elimination I isolated the lower ring final as the issue.The fault occurred after heavy rain here, and after exposing the socket tops I observed that box 6 was very damp with badly corroded conductors and switch connectors. I replaced the socket with new after treating the corroded cables, but still the RCD trips when the phase is energised. From the CU I have continuity and resistence as follows... L=0.43 N=0.43 CPC=0.7; the ring length I estimate at 45 meters in 2.5/1.5mm twin and earth. On my clamp meter I show 4mA leaking through the main earth bonding leaving the board. I did not do a figure of eight test as I only wanted to establish there was no break in the cable, as we do get mice here quite regularly. I am totally perplexed that I have continuity with correct resistence, but still the RCD trips. Here in South Devon we can't get electricians out for love nor money, so I'm hoping someone on the forum can point me in the right direction. Once this issue is resolved I plan to upgrade the CU to RCBOs for all the power MCBs. In case anyone is wondering, I am not an electrician but do have a background in automotive electronics so feel competent enough to tackle this stuff. Many thanks in advance.