Judith

No, not definitely. It wouldn't have cost much extra if we'd had it with the Genvex though. Not much extra to install, maybe much extra to run.

My short list of companies is so far: Genvex, Zehnder, BPC, Daikin, Vaillant, but still at a very early stage of research.

Heat calcs are 6kW (don't forget we were building in the 1990s), so the 4kW in the duct heaters was a deliberate undersizing. We don't need to heat all the rooms in the winter, and we have a lot of solar gain in the south.

I'll try and get more pics and more info.

Well that's interesting. It would take someone who knew what they were doing to decommission the heat pump in the Genvex, then hopefully it would no longer blow fuses. Do you know of any make of heating-cooling heat pump that could run inline with it?

Yes, yes he did, definitely. My mistake.

Thanks, but I don't think so. It functioned for years, no fuse ever went. Then last autumn we tried switching it on and it just wouldn't come on. I think it probably has reached the end of its life after about 24 years, and we need a new machine. I wonder what brands are on the market.

The capacitor cost about £30 to import from Germany. But despite the brand new capacitor, the same thing is happening again. The instant the machine is switched on, a fuse blows, a real one inside. They are very cheap but fiddly to put in. A sparks told us that it probably means the condenser itself is gone. We could have it degassed and removed, but then we would need a new condenser, which would be a different kind and wouldn't fit in the box. Maybe someone could do it, but not a DiY job.

There are three duct heaters. One does the basement lounge, and that's 2 kW. with a grid at floor level. Another at 1 kW does the kitchen-diner and the other at 1 kW the bedrooms, those all into the ceiling MVHR. They're on 3 programmable thermostatic controllers. We might replace them as well, as they are prone to cutting out unnecessarily and hard to reset. We could DIY that replacement or get a local sparks to do it. We are very upset about the Genvex failing BTW as it would have been repairable were it not that the CFC refrigerant is no longer legal (for good reason of course but we like to keep stuff running).

So that's 24 years, not 4. We have electric duct heaters in the ducts. No wet heating.

Installed 1999.

I will try to see. It was someone sent by Joule who fitted it, after the original person who set the machine up couldn't understand why it wasn't working properly (although he had gone through the steps in the manual and signed them off). There's a complication in who is ultimately responsible. Our contract was with a medium-sized electrical contractor who fitted the PV roof and the iBoost. But they bought the Joule from a smaller heat pump specialist company. They were all very nice people and we trusted them to get the teething troubles ironed out. But now the heat pump specialists, who never knew much about the Joule in the first place, have pulled out of air-source and are doing ground-source HPs only. The senior guy from the electrical contractor, who has tried the most to understand what is wrong, has given up on trying to get any info out of Joule. I probably need to contact him again, but they will charge full-whack even for a non-emergency call-out, so I am trying to understand as much as possible by myself beforehand. With the help of people here, much appreciated.

Thank you. As far as I can see at the moment it is not heating up at all on HP only. But I need to take some time to understand the programming system in the manual, to understand when it is meant to be coming on. I might be able to do that tomorrow.

Hi all. Our old Genvex 400 MVHR with heat pump has almost certainly given up the ghost. A capacitor was obviously no longer working, we replaced it (took ages to get it imported from Germany), but a fuse blows every time the machine is switched on. We understand that probably means the condenser is faulty, and it cannot be worked on because the CFC in it is no longer legal. So we are resigned to buying a new MVHR with heat pump for our space heating, this time I think with the "comfort cooling" option. All the ducting is still in place to re-use. What brands are on the market that we should consider? I see that Genvex is still available, but perhaps there are more choices now? Many thanks.

Hello again. The manual you linked to seems to be a later version of what we have. I've been observing what happens to the Joule. Even though I haven't yet fixed the error in the diverter it is still going to Error 11, never immediately, but often, and always during the night. I found previous notes where the electrician/heat pump person thought it was happening whenever the temperature went above 60, but that is not the case, as it has been at 62 and remained on for an hour or more. We definitely had a further immersion fitted into the tank, as my partner remembers it being shown to us; he says it looked like "a long piece of copper". I am going to carry on a little longer getting data and also try to see what the programme is doing, whether it is cutting out whenever the heat pump is being called on. I suspect it is probably not a question of regassing, unless that could have been the issue from the start. Three supposed experts have looked at it and all assumed that it was the attempt to control it by the iBoost that was the problem.

There is no dp switch or spur between the diverter and the Joule. I am doing some long-overdue diagnostics while the iBoost doesn't switch the machine on when the sun comes out. (The manual overrride does work.) I am seeing how long the Joule will stay on in heat pump mode. I cleared the error message by holding OK, as I have done so often. The error message is always E11, i.e. "probably something serious, ask an expert". Now the display is showing the water temperature, 56.9 deg. I will check it a couple of times this evening. The heat pump is timed to come on at around 18:00, and during the evening we will probably have used enough hot water so that it should. If all goes well we will have hot water in the morning. Your link to the instructions didn't work for me. The second immersion is not external. This is the only photo I can take that might give you any information. I suspect that the black flex is the usual feed to the unit, while the white one that bypasses the switch and goes into the back of the machine comes from the iBoost. We are in Brighton. Many thanks for your advice.

Thank you for all this. I will try to re-pair the sender and diverter, as that could indeed be necessary, despite what Marlec said. The sender and diverter are about eight meters from each other and there are only partition walls and furniture between them. They haven't had any problem communicating before. There IS a separate supply to the first immersion. That one is still in use, coming on periodically to bring the temperature to 60 to prevent legionella. The unit is supposed to be designed to allow for a second heat source, e.g. solar hot water, (our old Vanvex was too), and that is how the second immersion was installed. One hypothesis related to the fault is that the heat pump cuts out when the tank is heated beyond its target temperature, outside the periodic raising to 60. The engineer from our electricians has attempted to solve this by altering the target temperatures of the heat pump and the second immersion. And for a while in the winter that worked, i.e. it went for a week or so without going to error message. Right now, I can reset it and it starts to run again, but that only lasts an hour or so. I am becoming convinced that there is nobody in the UK who understands how to get the Joule Aero unit to work with a diverter. Although when we were sold it everyone was "sure, can't see any reason why not". If we were to bring someone in, who? We have recently been transferred from Bulb to Octopus and they are very keen on heat pumps. I was given the email address of their heat pump team and will contact them in case they can help.

Sorry I didn't explain correctly. The Joule with its tank is our only source for DHW. A Joule air-to-water heat pump always has an immersion heater in it as a back-up, and the idea was to connect the diverter to that. The heat pump is programmed to come on in the evenings, so we should get hot water in the morning heated by heat pump. Then on sunny days we should be able to use the PV-generated electricity to run the immersion. We were replacing a Vanvex air-to-water heat pump, so didn't want to go back to just an immersion, and we were replacing the PV roof. I hadn't heard of diverters until the electrical company who were doing the PVs suggested it. They brought in a heat pump company, who were assured by Joule there was no reason why it would not work. But it didn't and nobody could work out why. Eventually Joule sent a technician, who put a second immersion inside the Joule (it is designed to be able to incorporate it, or it could take input from solar hot water panels). We've had it all in for 4 years, and although it has been annoying that the heat pump part of the Joule constantly goes to error message, we are saving a lot of money heating all our water by solar.

I'm not sure that there is anything that I could take a photo of that would help. The Joule has an immersion heater in it when sold. A second one was fitted inside the unit by a technician who was sent by Joule. He said that would resolve the errors we were getting but it didn't. We have a user's manual about the control system but it is beyond me although I have done some programming in the past, and also beyond all the staff in the supplier (qualified sparks/heat pump technician/electrical-electronic engineer), and Joule have nothing else they can send. I suspect they don't know a lot themselves, and only import them. As I understand it, the extra immersion is controlled by the diverter and the original one comes on periodically to raise the temperature to 60 to prevent legionella, although it probably doesn't while the error message shows. Joule tell us we must have it serviced by them every year or we are non-compliant with the terms of the grant we received on installation; they say they have no responsibility as we haven't completed the servicing booklet which they never gave us in the first place. I suspect we will have to get an independent heat pump engineer round, but how to choose someone who knows what they are doing?

Thank you. It is Marlec, the manufacturer of the diverter, that said it was probably a problem with the thermostat settings on the immersion. I didn't tell them it was a heat pump rather than a simple immersion heater. In fact we have only been using one of the two immersion heaters in the Joule since the installer's engineer gave up on it a couple of years ago. They don't see to have lost connection. That would lead to a different error message. If they have lost connection there are instructions as to how to pair them again, but it seems to be quite difficult.

It was Marlec who said it was to do with the immersion. That's the only reason.

So this is our question about ASHP. We have a Joule Aero for DHW. (Space heating is, in theory, MVHR with an old Genvex 400 with heat pump, plus duct heaters, but that's a whole nother story). And we have a PV roof and a Marlec iBoost to divert excess energy to the immersion in the Joule. First problem is that this has never worked properly. As soon as the sun comes out or we manually select Boost, the heat pump in the Joule displays an error message and stops functioning. After advice from Joule, a second immersion was fitted, but that hasn't resolved it. Second, urgent, problem is that when we came back from a recent break the iBoost was displaying Sender battery LOW. T(he Sender is a small item near the consumer unit that monitors the electricity consumption in order to trigger the diversion to the heat pump.) So we replaced the ordinary AA batteries with brand new ones - in fact we did it twice to be certain - and it continues to display Sender battery LOW. We can still get hot water by using the manual boost, and can do it when the sun comes out, but there is no automatic diversion. I emailed Marlec and they replied "it would be advisable to have your immersion/thermostat checked out by an electrician as it could be a fault with that." Any ideas of what to do? Joule have so far not been helpful when contacted and the electrical company that installed it complain they can't get any manuals or advice from them.

That's good to know, Marvin.

Hi everyone Just joined this forum although we were on self-build forums way back in the 1990s when we started our self-build on the outskirts of Brighton. We are now at the stage when all sorts of things need re-doing on the house, this time usually working with builders rather than entirely with our own hands as before. We were early adopters of all sorts of technology, and have learnt the hard way. We are on our second photovoltaic roof for example. We have some possibly quite obscure questions about heat pumps that we will ask separately. Graham was originally a carpenter many years ago, but most of his career was in teaching. Now both retired. Thanks to all who keep the forum going. Judith and Graham