Beelbeebub

I think the issue is with air escaping. With a drop you essentially get air locks in the pipe. The water is trying to go down and the air is trying to go up. Paradoxically a bigger vertical might make it worse as there is more back pressure from the air lock before any horizontal section where the air can sit above the water. The idea of a tundish always confused me. I get there is a reason for them as an anti syphon device and there is a visual indication argument. Except the visual indication is useless if the thing is in a rarely visited cupboard and the antisyphon argument doesn't seem relevant if the pipe is leading directly outside or even if it's leading to a soil stack. A clear glass section with a properly designed air admittance valve would probably be better albeit more expensive than a tundish.

You can do that too, or you can pump the whole hot water supply - either way you need a pump. On the plus side newer inverter pumps are pretty quiet and can provide nice even pressure without the old on/off/on/of pulsing behavior of the old ones.

If you want decent hot water pressure. The vast majority of the properties I look after are flats so the tank is about 400mm above the shower head so the showers are rubbish. Wasn't a problem 40 years ago when people predominantly had baths but now people expect showers at a decent pressure (coincidentally we have seen a big rise in bathroom damp/mould issues as showers out in vastly more moisture into the air)

Exactly (this is what happened to us). In addition, the approved tundish allows a slight trickle of water to track around the support arms to the outside of thr tundish and onto the floor (again also happened) . I modify the tundishes so the copper pipe can drop 10mm or so below the stop o form a drop edge and stop this. These and various other problems with the venting are what has soured me on UVCs. That said they are neccesary for HPs - the only alternatives are thermal stores, which are inefficient for HPs and vented cylinders, which require pumps. Which it to explain why I keep thinking some sort of relaxation/rewrite on the regs to make it easier to install and actually work on the rare occasions thry are required to work. Now all immersion have the double thermostats/cutouts and boilers also have mutiple systems to prevent them boiling the chances of a boiling event are extremely low (though the consequences are still high)

Fair point

I'm more getting at the routing for the tprv rather than the usual stuff with inlet groups, expansion vessels etc which would all be needed. I'm coming from the perspective of the annual check needed for a vessel that could potentially explode (though most home owners don't get them serviced). If the vessel can't explode then the safety requirements are less critical. Actually, while I think about it, given a significant portion of unvented cylinders probably aren't serviced annually, have we ever heard of one exploding? Or even blowing off and injuring someone? I did see a myth busters where they deliberately sealed one shut and boiled it, and it did go off like a rocket. I'd have thought if that happened we'd hear about it.

Yeah but that's what the usual prv is for. The tprv for unvented has very specific routing and venting requirements to handle near boiling (potentially above boiling) water partially flashing to steam

Good point! The old "nail in the fuse box" fix.

Still not enough to boil a cylinder tho? And if someone fits a co2 HP capable of boiling a cylinder - then it's g3 as per usual. The exemption would only apply to HPs deemed unable to boil cylinders. Could even be a tick box in the spec where the manufacturer declares the HP unable to reach 95C in all fault conditions.

I guess the problem with a prv test is a proper test is to stick the immersion on and boil the tank, but that isn't really safe or practical. The units we had fitted had a knob on the top you turned and that would lift the valve, which isn't really a test of the system only to see if the valve would open. TBH fitting a burst disc would be the safest way but i've never seen one on a domestic system. They do need to get around to sorting the g3 regs so that a system only connected to a HP without any immersion can be treated as a vented cylinder since there is no possibility a HP can boil the tank. That would make installs easier

Years ago spoke to the technical director of reliance controls about "servicing" of their PRVs etc Context was a very awkward tenant who insisted that the valves be serviced every year and wouldn't accept that getting a g3 ticketed engineer to inspect and sign off the cylinder etc was sufficient. Upshot was, there wasn’t anything to "service" - you look at the valve, make sure nothing is blocking the pipework etc and there are no visible signs of leak/degradation. I asked specifically about turning the knob to activate the valve and he said you could but there was always the risk it wouldn't seal back properly and you'd have a persistent drip, which would mean the valve would need replacing. From the safety POV the main thing is that the valve opens when the pressure or temp are too high. They are engineered to be highly reliable and fail safe, ie anything that goes wrong makes them open easier than design. The servicing is more to check they aren't leaking and the venting arrangements are still adequate.

I would suggest that headroom is less important for such a large house. Say we have a very cold snap and your 12kw heatpump isn't able to keep the entire house at 21C (or whatever the design conditions are) Just turn down a few of the unused rooms to 15C for that period. If you have a 2 bed flat and all rooms in use all the time you don't have that ability. But for such a big house the spare rooms can be hibernated for a bit.

5 years is a bit on the short side but I have had multiple ones fail, it's one of the most common things to fail in the heating systems I manage. Prob have one or two a year out of 35 or so.

Which part of the system is that leaking tundish linked to? Is it the domestic hot water or the system loop? Is there a pressure gauge for the DHW tank? There are 2 reasons water is ending up in a tundish. 1) the valve is faulty, the seal may have hardened ornvt some debris on the seal. 2) the expansion vessels are faulty allowing the pressure to rise too much and triggering the relief valves (as they should). It would seem to be very unluck to have both loops (system and DHW) faulty at the same time So the first thing is to note the cold pressures of both the system loop and the dhw tank. The system is typically 1-1.5bar cold and maybe 0.5bar higher when hot. The relief valves are often 3bar (but not always - it should say on the valve) The dhw cold pressure will be your mains pressure, that can be anything up to 5bar, though often 2bar or so. Again, when hot it should be 0. 5 to 1 bar more and the pressure relief will typically be 5bar or more. If the pressure on either system is rising by more than 0. 5-1bar it might be the expansion vessel. If the pressure isn't rising above the value marked on the valve but water is passing then you prob have an iffy valve - they are designed to fail safe i.e. leak or open early rather than open late. If valves are faulty (activating before design pressure) they need replacing by a g3 certified plumber. Very occasionally they can be cleared by activating them *if* the issue is debris on thr valve seat. If the vessels are faulty (big pressure swings) it could be thry are simply out of gas - tyre pump to refill or they could have ruptured the membrane, in which case new vessel.

One possibility is that - for whatever reason - the system was drained down during the servicing and air entered the pipes. The plumber will repressurise but as some of that trapped air gets circulated around it will eventually find it's way to an automatic air vent, either in your pipework or in the heatpump. As that bleeds out you can get a drop in system pressure. Some systems can take quite a while to purge themselves and require a couple of top up cycles. My own system takes ages to get rid of all the air, but that's because it's crap.

Yes but if the vessel has never been topped up from new this shouldn't be a possibility as they are generally precharged with dry nitrogen - strictly speaking they should only be topped up with dry nitrogen, but nobody bothers. There would only be enough water from condensation to squirt out if it had been topped up a few times, which would indicate an issue somewhere (eg leaking prv) anyway.

If the system pressure target is 1.5bar when cold, then your pressure vessel should be at a little bit below (say 1.4bar) when empty. This allows a little water into the vessel when at system pressure and the maximum volume change when hot. So if your water pressure gauge shows 0.2bar your vessel should show 1.4bar. Of it shows lower then the pressure is wrong. You can top it up but the fact the air has been lost points to a failure in either the valve or the internal membrane. If some water comes out of the valve, your membrane is almost certainly shot. Swapping the vessel is the easiest.

2 possibilities You have a leak somewhere You may have an issue with the expansion vessel (red tank) First check the expansion vessel When the pressure is near zero, like in the first picture, get a tyre pressure gauge and read the pressure in the red cylinder. There should be a valve exactly like a car tyre one on the top. It should be something like 0.7bar, 1 bar or similar. If it has pressure eg 0. 7bar but the gauge on the water reads near zero, it is possible you have a leak somewhere. If it reads near zero your expansion vessel has lost has pressure (you may still ha e a leak but it's a bit less likely) If the latter you can pump it up with a.tyre or bicycle pump. Then top it up with the flexi hose. You need to turn the. Slotted screwdriver thing so it's. Inline withe the pipe, then turn the black handle at the other end. There should be a whooshing sound and the pressure creep up. Once at desired. Level (1 - 1.5bar) turn both valves off and disconnect the pipe (get a saucepan under as some water will come out. Beware just topping up the pressure continuously. The water is going somewhere!

You usually need to buy the camera too, I use thr "top Don" one, it just plugs into your phone and away you go.

The ufh should be able to get those rooms warm if it did before. The flow temp shouldn't be very high ie a HP should be able to achive the temps. My suspicion is too. Much flow of going via the radiators, which is shutting down your HP, the UFH then doesn't have a supply of warm water to "top up" the loop temp via the mixer valve and then they underperform.

I had a cottage where the radiator in the hall was absolutely scorching and all the other rads were like warm. The boiler short cycled and lots of gas was burnt. We closed the valve on that rad right down and all the rads became warm, the boiler stayed on for long continuous burns and the cottage was warm for not much more money

As I said the other option is one rad being "too open" and starving the other ones.

Either your emitters are very undersized - thr ufh loops should be OK, the whole. Point of ufh is it being a big emitter. Maybe your rads are too small? What type are they? Single panel, finned? Double panel double fin?. How big are they? Rads for HP should be bigger than what is typical in a boiler heated house. Your plumber should be able to tell just looking - 'they look bigger than I wound expect" or "nah, looks. like I. Would expect for a gas boiler house" (ie too small!)

Potentially the Vito boiler was supplying higher flow temps and each emitter was outputting more. This is why radiators and pipes sometimes need to be swapped for bigger ones when a HP is installed. Get an IR thermometer (better yet an IR camera for your phone - can use it to track down heat leaks in the walls too) Check your rads, your (heated) floors. Is there a rad that is especially hot, in particular if it's flow and return are very close - they should be 5-7C different. It's possible one of the rads is "short circuiting" the flow, which cause the HP to shut down (as the flow and return are too close) and your overall heat output to buikding is lower plus less efficient because of start stopping.

Link to the manual. https://trade.centralheating.co.nz/assets/resources/Chofu-Operating-Installation-Manual.pdf