Nickfromwales

Have you fitted a non return valve ?

Hi Damon. Good to see you posting here. Apologies for the glitch.

GSR’d fitter required if the case you have to remove to get access to the duff part forms part of the air / flue / combustion chamber. Look for any notes in the MI’s that state any disturbed seals need to be replaced. I would concur that it’s a PCB fault as it sounds like a relay has gone grotty and is allowing voltage through when energised but not when in the ‘normal’ state.

Just bin the thing. If it went anywhere near prematurely it’s probably down to continuously rubbing against a surface imperfection on the inside of the vessel. Move on and don’t waste time / money, they’re just too cheap to buy / replace.

The noise comes from the unit itself in most cases. I’m routinely fitting Brink units atm and they’re really well respected ‘in the industry’ as the weapon of choice ( when PH certification levels of quiet are the requisite ). Brink do a range of bolt on ( manufacture specific ) silencers now, so I’m going to trial those and see how they compare to the normal / knee-jerk flexible acoustic attenuators in real life. Current ones I’m fitting in a high-demand dwelling are the box attenuators which are a metre long !!! Bloody big game of Jenga currently going on in that plant room ! Compare apples with apples here though, as some MVHR units have integral heat pumps for auxiliary heating / cooling, which are noisy if not high - specification units, or standard MVHR units with just heat recovery which are very quiet out of the box.

Maybe to remove metal from a cold ventilated space? Even though they’re not in ‘direct contact’ maybe it was a wise precaution.

As long as it’s metal and CE marked them it should be fine. Fitted plenty of “double-decker” CU’s in the part.

@AnonymousBosch Steer clear of MK. I’ve heard from my spark and other merchants that their possibly disappearing off shelves some time soon.

£1000 / £250 = 4 RCBO’s then. Plus the CU itself. More like a £2500-£3k CU.

Not as crazy as it first sounds for sure. Especially when you have freezing cold water entering a porcelain cistern in a warm house. TBH, if I was providing for that remit I would fit a local accumulator ~30L to blend ambient temp water with the incoming cold to provide some uplift. Or tank feed the loo.

Just simply adding more stagnant cold water volume between the boiler and the hot outlet. It's only really problematic for the basins / sinks where high frequency / low volume consumption occurs.

It’ll also heat the cylinder faster ?

Get a 15kW boiler and set it up as W-plan ( DHW priority ) and the boiler will only ever do heating OR hot water, and never the two together ? edit: agree to oversize slightly and go for an 18kW unit.

If they get supplied directly, from source, and on 15mm supplies then probably not that much more of an impact tbh. If you have separate isolatable runs from source anyway, is there any actual need for the manifolds ? ?

Ah, my apologies. I thought you were manifolding the hot and cold water system. D’oh!! ?. FYI I do that routinely on my projects. ? hence my knee jerk response. Manifolds for the heating will be fine. ?

Very little when it’s designed in. The Vaillant has the 2x PH tanks fully encapsulated in EPS to minimise losses. Would be greater if added retrospectively or done on an UVC / other, but Vaillant have had to do that to maintain ERP rating. Honest answer would be run yours for a quarter and compare bills.

Just use 12mm plywood, glued and screwed, but make sure the floorboards are securely fixed down before doing anything as nothing will stay down if there’s movement in the subfloor. Any movement at all. The plywood will form to the undulations better than a rigid / brittle product will, or, lay the cement boards into cementitious flexible tile adhesive and screw down when cured. For the record, I’ve not used tile backer board on a floor. Never ever, and I’ve never had a floor break down because of it. I just don’t like the flexible vs brittle marriage at all. I’ve used the 1/2” thick one to make wet areas up / walk in showers etc, but that’s it. Not lost a patient yet in nearly a 1/4 century of tiling.

15mm inlet on the combi = total waste of time putting 22mm on the outlet. The only reason you’d go to 22mm would be to reduce resistance over a VERY long run. To be honest, utilising manifolds with a remote combi is not a very good idea IMO as you’re adding a huge amount of dead leg to each outlet, particularly the basin tap ( high frequency / low volume use ) which will be a PITA. If you want some divisibility then you could do 2x 15mm runs from the combi 1x 1st floor 1xground floor / whatever best divides the system, and just have an isolator ( FULL BORE ) at the combi for each run. The Vaillant 938 is a fantastic boiler with IIRC a 15L pre-heat cylinder ( actually it’s 2x 7.5’s for less physical space requirements ) and is comparable in DHW delivery to a 200L UVC. It’s only Ach’s heel is it’s still only a 15mm inlet & outlet, but with a good cold main you really can’t tell. The time from opening an outlet to actually getting premium temp DHW is massively reduced as it’s always got that buffer ready to go, so definitely a contender for anywhere where longer DHW runs will end up causing inconvenience. Veismann combis seem to have a good following but I can’t really say I’d rate them over the Vaillant if I’m honest. Guess I’m biased because I’ve fitted so many of the Vaillant units without an ounce of grief. Adding a DIY hot return to a heat store boiler will, I’m pretty sure, void the warranty. Ring the various manufacturers to ask, but I think the only heat-store combi I’ve ever seen with a tank and a hot return tapping was the Arirton 27 Plus ( a steaming bag of shit on a good day though, and I’d only fit one for someone I disliked ). The 27 Plus was the old model, they may have renamed it since I saw one of them last. Vaillant 938 all the way if it was me.

Not really, with a combi. You can take the edge off a little with a pre-heat aka warm-start combi where the boiler fires intermittently to keep the DHW plate heat exchanger at premium temperature, thus staving off the time you lose waiting for the boiler internals to heat up from cold ( eg the time lost waiting for the premium heat delivery temps to be achieved and output from the combi DHW outlet. Bottom line is NEVER have 22mm DHW pipe work from the boiler to the outlets.

Expect a long delay in getting premium hot water out of the hot taps, especially the furthest away. Other than that, no issues whatsoever. Check with the boiler manufacturers installation instruction to see if the boiler has an in-built frost thermostat or whether it is down to you to buy and install one. If the room is prone to super low temps at the worse part of winter, fit an electric tubular heater with its own frost thermostat. Set the boiler frost stat to 7oC and the tubular heater stat to 10oC.

You could fit a natural gas ‘hybrid’ air source HP and a pair of size 12 HW+I Sunamps, with the SA’s doing hot water only. The SA’s are fitted with 3kW immersions so you can heat the SA’s off cheap rate grid electricity plus you will have boost / failsafe options to boot ( eg full DHW capability still available even if the ASHP goes offline ) plus you can also heat them off the high temp HP via the hydraulic heat exchanger. The 2x SA units will give you the equivalent DHW capacity of a single 600L UVC but with no G3 requirements or annual maintenance schedule ( and related annual inspection costs ) plus very low standing losses compared to traditional cylinders. Have the SA’s set to heat once a night on economy rate electricity ( E7 / 10 ) via the immersions to deal with the bulk DHW requirement with near zero system fatigue / maximised overall system longevity ( as the ASHP will then be moth-balled most of the year ) and just use the HP to top up DHW during the daytime if required. The SA’s ( 2x ) will hold around 26-28kWh of heat energy so will provide probably 8-9 of the daily showers, with gas+hybrid bridging the gaps only. As it’s basically a “commercial” installation in what appears to be an HMO, system longevity ( and increased reliability ) will be an important factor. Remember this will attract ‘non-domestic’ RHI which is a 20 year period but at a lower £rate, so I would look closely at preserving the capital expenditure by increasing the lifespan of the system vs trying to squeeze every ounce out of the RHI as replacing the equipment early will neutralise any benefits thereof. Great that you have wet UFH aka low temp emitters on the ground floor, as ideally you’d have the HP provide space heating at as low a flow temp as possible ( to avoid the gas element of the hybrid kicking in and therefore maximise the CoP ). What about your intended solution for 1st & 2nd floors space heating emitters ? If rads then they need to be over sized to give useful heat at lower flow temps. Alternatively, you could fit 10x 8.5kW electric showers and upgrade the electricity supply ( if there isn’t already 3-phase on site that is ), and then just fit a small 150L HP UVC to provide the rest of the DHW needs ( sinks and basins ). Regardless of the way you provide DHW you will definitely need to boost the cold mains with a single or pair of cold mains accumulators to get anywhere near running a few of these showers simultaneously ( plus allowing for WC’s being flushed / basins being run / utility taking cold water etc ) or, which you may already be planning, each self contained dwelling would need its own cold mains supply ( & meter ) to keep up with peak cold mains demand. Early system planning, and consideration to everything else that will be needed to fortify your base question will be of paramount importance Pointless having a whopper of a DHW system if there’s nothing to force that water out of the outlets ( particularly at the 2nd floor height ). Another option is separate the DHW and heating, as above, and fit 3x 12’s and a pair of low temp ( regular ) HP’s for space heating only. Really needs some numbers crunching tbh. Confirmation on the situation WRT electricity supply 1 / 3 ph would help. 3-ph HP’s are available. ?

Impeller even ?

It’s a small propeller type spindle that you can buy as a spare for a few £10’s. Easy enough to change too. https://rover.ebay.co.uk/rover/0/0/99?loc=https%3A%2F%2Fwww.ebay.co.uk%2Fp%2F2256002575%3Fiid%3D173512321204 Try that first and go from there ??

It’s item 19.

Vado is a little over priced, but it’s an entry level ( decent ) brand with good ongoing support / spares. Next jump is typically to Grohe / Hans-Grohe stuff which is legendary stuff. I’ve fitted mountains of both with no recollection of issues with Vado. Is this still a mixer or two separate taps? Beware moving away from a mixer tap as the hot tap just becomes unusable / unbearably hot unless a small TMV is fitted to manage the max temp.