jack

Standard wet UFH (ie, screed on insulation, UFH loops in screed). I believe they're going for engineered wood on top, but not sure whether that's a definite.

I got hold of the model number. According to the data sheet it's inverter driven (note: I may have been misremembered the comment about the short circuit being on one coil):

Latching would seem to make sense, but apparently the tech support guy was adamant that the light only operates in real time. Yes, all the electricians who've seen the installation agree, especially given the low loop impedances that have been measured. According to my father in law this morning, it's only 4 years since they moved in (I was convinced it was 5). It's a new build and the ASHP was new when installed. Would Mitsubishi still have been selling non-inverter-driven ASHPs at that time? I'll see if I can get the model number and check.

The fly in this ointment is that surge protector's tech department insists that the warning light doesn't latch. That means that if you see the light, there is an ongoing voltage difference of at least 30V between N and E. I don't know how long that was present for, but it was at least hours. In fact, I think my parents in law said it was still flashing the next day. I can check. It's also possible the tech person has this wrong - it would certainly make a lot more sense if it latched (and make it more plausible that the ASHP motor failing caused the problem).

My electrician's just dropped by for a cup of tea and a chat after finishing up for the day. It seems that the ASHP compressor motor has packed up, with at least one dead short across one of the coils (not sure if more than one). The noise filter has packed it in, and another control board is also suspect. One possible scenario is that the short was initially intermittent, resulting in high speed switching within the coil. The thinking is that this might have caused spikes that have caused the damage. Again, this doesn't seem particularly likely, but it's no less plausible than any other proposal currently on the table. Oh, and it also doesn't explain the >30V fault that was seen on the surge protector. It was, however, established that this protector wasn't installed correctly, as it's much too far from what it's supposed to be protecting (not that this explains the 30V fault light). The next step will be a full house inspection to see whether there are any other issues. Between them, my electrician, the other electrician (works for the company that wired the house), and the ASHP guy have decided that a separate surge protector at the ASHP would be a useful thing to have. I think we'll also install an RCD on the incoming three phase main. Thanks again for all your help with this. It's clearly an unusual situation, as everyone is scratching their heads about how something that measures so well now can have behaved so badly only a couple of weeks ago.

I believe they've asked around, but not sure how far afield they've gone. The next door neighbour also has three phase off the same cable on the street and they've confirmed no problems during the periods when the damage happened.

One of electricians floated that as a possibility - long dry weather followed by rain causing some sort of intermittent tension on the joint. Conclusion was that it's possible but unlikely to now have become completely undetectable. I don't really know much about power electrics, so I can't really follow the details of what the electricians were discussing, but could it be that a break in the PEN results in the additional bonded earths at the house becoming the return path for the respective live phases? Not sure... No-one's quite sure exactly where it is! But we're on fairly sandy soil here, so water tends not to hang around in the soil for long. I doubt it would remain immersed for long periods, but not sure. Yes, that's right. It is a puzzlement, no doubt. All possibilities so far identified seem to be very unlikely, but something has to have caused all of these issues in two separate events separated by weeks. I'll let you know if we learn anything more once the ASHP guy's done his bit.

UPDATE I've just returned from the house. My electrician is there with an electrician from the company that installed the wiring and surge protector. It's presently a complete mystery. All measurements are coming back clean and well within range. Loop impedances are all rock steady at around 0.19-0.20 ohms. All connections appear tight. Currently there's some speculation about whether the ASHP could have been failing and somehow dropping a large spike back when turning the compressor motor off. Possible but seems unlikely. Another (probably even less likely) possibility is a joint in the front garden. 5 years ago, the landscaper broke the incoming main, and a joint was made and buried. It seems possible that there's an intermittent fault between neutral and earth at that point, although consensus seems to be that there should be some evidence of that even if it isn't in full fault mode right now. All of this is genuinely just speculation right now, and there's a lot of head scratching going on. The ASHP guy was running an hour late, and I had to leave just as he arrived. I've asked the electrician to let me know what else they find in due course. Oh, and there's definitely no RCD on the incoming three phase. One of those will be installed as part of all this, although naturally that won't address whatever the actual problem is.

Thanks for that David. I've told them to make doubly clear that they aren't claiming, and I think they're on it (father in law runs a business that includes delivery vans in London, so he's had a lot of experience with insurers over the years!) I don't think they're too concerned if it isn't covered - the main thing at the moment is identifying the source of the problem so they aren't potentially throwing good money after bad.

Thanks Dave, I'll mention it to my parents in law.

Exactly. In fact, my understanding is that they only contacted their insurer to let them know what's going on, and not to lodge a claim at this stage. They just heard that the insurer was sending someone anyway. I don't know more than that. More generally, I'm encouraging them to focus on identifying the problem before doing anything else. Until that happens, it's pointless (albeit human nature) trying to plan the next move.

They've spoken to their insurer, and the loss adjuster is coming out on Friday with an expert. If possible, they want to know what's going on before then, hence getting someone independent involved now. Whether their insurer will pay for this electrician's time, I'm not sure. I think they're happy to pay themselves if needed the main thing is getting a clear identification of the problem.

I think I saw that in some paperwork they had out. Will check. They mentioned that they'd seen something about a "platinum" warranty from NICEIC, but as you say, it's a long time to be claiming on a warranty. The main aim at the moment is to find the source of the problem. If that can be sorted, and it isn't an obvious installation error, I think they'll be happy just to get a definitive answer so they can rest easy living there in the future. Edited to add: the potential for blame and arse-covering is a major reason for me suggesting getting a neutral (pardon the pun) electrician involved in identifying the problem. The guy I've asked to do it is very thorough and has no axe to grind. He'll give an honest answer without fear or favour.

No idea. It's a 5 year old Mitsubishi - I've always assumed that an ASHP from a mainstream brand of that era would be inverter driven. At this stage, we don't know what's actually fried. It might be just a small control board. I'm sure all connections will be tested thoroughly this time!

The SSE guy has worked for them for over 30 years, and I think a lot of people who've been around a long time call it PME since it's what they're used to and it's perfectly adequate for most applications. I seem to recall a significant argument about the distinction on Buildhub in the past! I don't know. Best I can recall, they all varied relative to each other, but I wasn't really able to look closely to see what sort of scale was involved, and the SSE guy didn't seem too concerned about what he saw. My surprise was mainly that he seemed content not actually knowing what the problem was. This was clearly a serious event, with smouldering/buzzing from at least one AV component (Sky box maybe). As a matter of safety, you'd have thought he'd have advised finding the fault as a priority rather than just trying to get the lights back on. Will do, thanks.

Interesting, thanks Dave. The results SSE was measuring gave range of something like 235-250V over the time they were monitoring, so I assume they must have been measuring to neutral. I was astonished to learn this morning that the electrician who's been out so far (from the company that wired the house originally) has spent only a couple of hours onsite, all of it spent seeing whether he can get various things like lighting going again. According to my parents in law, he hasn't done any further testing that they're aware of. There was talk (prompted by my father in law) of them giving the electrics a general health check, but based on what I've seen so far I've discouraged them from using these guys any further. Thanks Jeremy. It's on the outskirts of a suburban area (just around the corner from where I live). The SSE guy said this morning that was a PME scheme, which was part of why he found what had happened surprising. I believe it's tripping its MCB. By 3 phase RCD, do you mean an RCD protecting the three phase as it comes in? If so, then I believe there isn't one connected - the SSE guy mentioned this morning that getting an RCD on the incoming three phase would be useful, quite aside from the other issues. I'm not really up on all of this stuff, but I couldn't actually see any RCD protection from a 10 second look at the CU. I may just have missed it. I'm sure my electrician will be able to tell me more tomorrow - I'll be onsite with him for the first hour to see what I can learn. This is exactly what I've already recommended to my parents in law, and what the electrician (the guy who you met when you visited) will be doing. I'll let you all know what we find tomorrow. Thanks as always

Thanks. I should have said, there was no nasty weather of any sort anywhere near when this happened. Lightning was the only thing I could think of, and we've written that off as a possibility.

Thanks very much Jeremy. If that isn't too much trouble, I think it could be a very handy tool. The "how much insulation under my UFH" question comes up time and again, and it would be nice if we could show the energy and financial impact of doubling (for example) the minimum building regs spec. Happy to help - please let me know if there's anything I can do. Thanks

My parents-in-law moved into a newbuild house about 5 years ago. It’s a large house with quite a lot in the way of electrical gubbins, including (3-phase) ASHP, wet UFH, a Control4 home automation system, electric gates, etc. They had an issue a couple of years ago with the electric gate control board blowing. They also lost a control board for their electric garage door. However, these seemed to be one-off issues. That changed about 3 weeks ago, when they suddenly lost several devices in their house at once. This included all of the electronic valve actuators on their UFH manifold, in-room controllers for the UFH, the gate control board and a few other bits and pieces. The company that wired their house and installed the Control4 system visited, and concluded that some sort of surge appeared to have taken out these items. All were replaced, and a surge protector was installed right as it comes into the consumer unit. Unfortunately, about 2 weeks after this happened, the wheels comprehensively fell off again. This time, the lights started flickering periodically one evening at around 9 pm. By just after midnight, a large number of electrical items appear to have malfunctioned, including all of the items mentioned above, as well as two sky boxes (smoke coming out of one of them), the electric garage doors, the lighting system, the mains-powered water softener, the boiler (apparently the fault code suggests the fan has blown), the ASHP and various other things. The surge protector indicated a fault at this time. I’ve just learned that the fault code indicates a voltage between neutral and earth exceeding 30 V. We’ve just had the DNO (SSE) visit this morning to check the voltage logging equipment that’s been in place since shortly after the latest problem. We had a look at the trace, and there is no unexpected behaviour over the time that they were monitoring. Of course, if the problem was intermittent, this would be expected. However, the SSE guy said that he had reviewed all of their logs for the last month, and there is no evidence of anyone else in the area suffering from problems, nor were there any local network problems logged during that period. Checks with other neighbours (including their next-door neighbour who is also on the same 3 phase supply) confirm that no one else has suffered any problems during this period. Of course, nearly everything is still turned off at the moment, so if there is a problematic circuit or device causing the problem, it’s presently disconnected. The SSE guy said he'd never seen anything quite like this in over a decade of dealing with SSE fault complaints. I have the electrician who did my place coming over tomorrow to see if he can get to the bottom of what’s gone on. However, from a chat with the SSE guy this morning, it really isn’t immediately apparent what could be causing such significant issues (including smoke and pop/banging failures) to so many different installed devices. I had a very quick look this morning, and it seems that the devices are not even all on the same phase of the 3 phase power supply. The only device that is connected across all 3 phases is the ASHP. It failed during this latest event, and now cannot be turned on without immediately tripping the circuit. It didn't fail during any previous event. Given the extent of the damage, my parents in law are naturally very concerned about the situation. There’s the obvious safety concern if a specific problem can't be identified, but there’s also the potential costs associated with replacing all of the damaged components. Of course, these can be claimed on household insurance, but if the problem returns, I suspect their insurer may be less than happy to pay out again. Based on the admittedly technically light explanation of the problem above, can anyone think of a possible mechanism that could lead to the outcome above? The ASHP engineer is coming by tomorrow morning to install a new board in the ASHP. Is there anything I should be asking him in relation to this situation? Many thanks as always.

I've been talking with some friends of mine who are in the middle of gutting and extending their house. We were discussing insulation, and particularly underfloor insulation given that they're replacing all their downstairs flooring and installing UFH. At present, their builder is doing standard building regs structure of concrete, insulation (is 100mm rigid standard to meet current regs?) and screed with UFH on top. I was thinking about how to compare the impact that better insulation would have on costs. Jeremy's excellent heat loss calculator potentially gives some clues, but I suspect that it works better for highly insulated houses where the air temperature (one of the required user inputs isn't much above the floor temperature. For a standard building regs house, for example, I assume the floor needs to be quite a bit warmer than the intended room temperature, so there'll be more losses through the underfloor insulation. This general question comes up quite a bit, and I think it would be nice if we could come up with a spreadsheet that lets us convincingly show the energy and financial impact of different floor buildups in different houses. I'm happy to have a go at this (@JSHarris, if okay with you I may use your heat loss spreadsheet as a starting point). However, I'm unsure about how you'd go about calculating the necessary floor temperature to achieve a required heating output. I suspect that to do a proper job, you'd need a combination of Jeremy's spreadsheet to get heat load, and then work backwards to determine floor temperature. It may, however, be possible to simplify this by making some assumptions and reasonable estimates. Any thoughts on this before I have a go?

Interestingly, I just downloaded this. Previewed fine in file explorer (Win7 box) but said it was a corrupted file when I tried to open it. I shut down Excel (I'd had another file open at the time), tried it again and it worked fine.

We thought long and hard about something like this for our house (my wife was very much in favour), but I just didn't see the benefit. I think I was right in the end: the one we were thinking about would have gone in the main bathroom, but frankly, our children manage to leave a trail of clothes throughout the entire house over the course of a day.

Can't remember (blocked it out!) but I believe it was over 100 £/m to supply, lay, powerfloat and polish the concrete top layer over our base slab.

Aldi specials this week bizarrely include an £899 thermal imaging camera. I know it's always a bit random what they stock, but how many of such a specialist item are they really likely to sell?

Whenever I look at wiring, the word "blue-tral" (blue = neutral) immediately jumps to mind. It's something I made up years ago to try and remember the colours for live and neutral. Everything else follows directly from that. Funny how effective memory techniques can be. I still have a mental image of a (steel) army truck blowing up, which I used in A-level chemistry as a way of remembering that metallic elements want to give up electrons. I also remembered F=Bqv (force on an electrically charged particle is magnetic field x charge x velocity) because we were doing Macbeth in English at the time, and "Bqv" reminded me of the character Banquo for some reason. Weird how the brain works...