SimonD

I would humbly suggest that you employ a water engineer that sits you down to have a proper think about the real world water demands and whether all the outlets are actually going to be used at once 😉 I know it's not what many want to hear on BH but the reality is that when you sit down to work out the real patterns in a house the concurrent demands are less than most people think. You've also got the pesky building regs and resultant design guidelines suggesting less water use per person. I know I've said this before but when I designed my system I started off in the same trap. I thought I needed to supply 3 bathrooms concurrently blah blah.However, instead of looking at upgrading the mains supply and accumulator, hot water recirculation and so forth, I looked instead and reducing overall flow rates while retaining pressure so even with less than 30l/min peak flow I can supply all bathrooms and whatever outlets without anyone complaining - although my only complaint is that I feel the kitchen tap (which comes restricted to 6l/min as standard) doesn't fill my pots quite quickly enough when I'm in a hurry. Our current main drench shower is regulated to 6l/min and it works really well. This approach was in part inspired by comments made by @markocosic to a thread I started a while ago about a similar question. Just fundamentally changed how I looked at the problem. You can also use 10mm pipe for toilets, basins, dishwasher, washing machine which also reduces impact on flow.

This is a curious thing. Do you have any of the design documentation for the ufh at all? This may have some info on design flow rate for your particular installation. Also, what wiring/control centre does your ufh use? What brand ufh is it? If you run the ufh on its own from a completely cold system, what happens? I'm certainly not inclined to suggest going to the expense of any buffer - plenty of these kinds of systems work just fine without them. Given that you've nearly got 30C flow return differential, you're on the brink of an error code so to meit points to a flow problem. My inclination would be go back to the basics, which is to make sure the ufh has been installed correctly - that all the plumbing bits are where they should be and functioning as they should and the same for all the related electrics and controls. Even really simple stuff like making sure the actuators are really working. Then also make sure it's balanced. UFH systems can behave really strangely if just one thing is off. I recently 'fixed' a whole house system in a relatively new build where the ufh was constantly calling for heat and bringing some rooms up to 38C even with the system set to summer mode, meaning it shouldn't be on at all. I noticed that about 4 actuators had popped off their clips which had broken. Manufacturer tech support said I should test all the room thermostats within the wiring centres etc.to make sure there weren't any errant voltages but I decided it best to get the actuators back in place first and then see what happened - as soon as they were back in place, the whole system worked again as it should (which logically shouldn't have been the solution). None of what is going on suggests a blocked heat exchanger or a problem with your boiler, it's somewhere outside in the heating system. But it may be amplified due to a high output boiler with relay control meaning there's no modulation.

Grundfos sell a number of different 'home boosters' a couple of which have accumulator tanks. Typically the accumulators do act as a break tank from the mains. As @markocosic has suggested, maybe look at a non pumped version. You'll need to decide how long you need the pressure boosted for as that will determine the size of tank. The Grundfos Home Booster tank is pumped and has a usable capacity of 180l @ 0.5 liters/second so about 6minutes worth of boost. Noise level is 65 dB(A)

Pressure and flow are completely different things. Increasing pressure does not necessarily increase flow. However, the main issue is that your installer should never have installed an UVC with those kinds of figures - it was never going to work very well. The water regulations also don't permit the use of a booster of more then 12l/min directly connected to the mains, so if you want to boost flow above this you have to have a break tank installed, so some sort of accumulator or a cold water storage tank with a pump.

You could also look at Tikkurila paints like the Optiva 3 Ceramic Extreme Protection which is even London Underground approved. With some reviews here: https://www.thedecoratorsforum.com/the-best-flat-matt-emulsion/

Yup, it's a bit of a sh*t show. Do the meaurements I suggested so that we know flow and return temperature rise over time and can then assess differential within each circuit.

Yes, do the tests and then we have some data, otherwise it's all speculation. Right now we have either/and: - a problem caused due a flow problem somewhere within the system; - a simple issue of short-cycling due to low volume of the ufh; The system bypass isn't really relevant as that's just there to prevent a no flow situation through the boiler when trvs are fitted to all rads. Some boiler manufacturers specify a minimum bypass length (e.g. Worcester Bosch say 3m on some models) so that there's a minimum heat loss through the circuit - but that's not relevant right now, nor is it relevant to the boiler short cycling as @JohnMo has said. Other questions: Does your boiler make any funny noises just before it turns itself off? Have any of the engineers suggesting a new boiler even mentioned a heat loss calc to correctly size the new unit and mentioned selecting a boiler with good modulation ratio? Have any of these engineers mentioned that it's the controllers that govern boiler modulation rather than the boiler itself? E.g. the Vaillant VRC 400 weather compensating control for Ecotec boilers that adjusts flow temperatures according to a heat curve and heat demand?

I think you can probably ignore the hot water system for now and just run the heating system so you have all rads plus ufh, then all rads no ufh and then no rads and just ufh basically so you're monitoring each zone. That should give you a reasonable picture to start with. Every 5 min or so should be fine. You want to be taking these readings until you see the boiler cycling. It's a bit tedious I know...

First do the investigations to get the data that supports the decisions. You can get the flow and return temperatures from your boiler yourself - d.40 for flow, d.41 for return temp. Run your system fully open and log readings over a period of time, then methodically close parts of it down while taking recordings over time, including the ufh only.

The op says about engineer looking at the ufh: "he was not 100% sure where the issue lay. He said there could be a blockage somewhere and/or the heat exchanger could be partially blocked." In any case, the flow rates need to be checked and confirmed and in relation to the temperature drop across the system - is the boiler cycling because there is too much temperature differential still (and corresponding low flow rate) or because the temperature differential is too small? I'd want to know this information. In each case a buffer cylinder could be of benefit, but it may need to be implemented differently is each instance. In one it may be necessary to differentiate flow rates between heat source and heat emitter where they need to be different, and/or to buffer the excess output from heat source that can't modulate down enough for the current heat loss.

Plastic - layflat polybutylene myself. Some copper in places. I prefer to use polyplumb pushfit now over both Hep20 and Speedfit.

First you have to diagnose the cause of the error message and that's only by a process of elimination. A competent heating engineer should be able to do this, but it does take some time. Then, if indeed a flow problem has been found somewhere on the system then this gets rectified accordingly. Sometimes it can be caused by a faulty fitting, sometimes due to crap in the system. Again, it's a process of elimination. For me the best tool I have for this is an infrared camera that immediately picks up temperature differentials in the system which will helps to zone in on where the problem lies. You need a cogent explanation of what is going on which means a proper assessment of the functioning of the whole system. Only then do you proceed with spending money on new bits.

High difference between flow and return temperatures is usually caused by a blockage of flow in your system somewhere, not the boiler - the boiler is shutting off due to the low flow. Short-cycling is caused when you don't have enough temperature difference between the flow and return but the flow is sufficient through the boiler. They are different problems that need to be separated. Get the flow problem understood and resolved first before spending money on a new boiler or a low loss header. Nowdays a heating engineer should really be doing a heat loss calculation to appropriately size the boiler as part of the replacement job.

You can but there are rules. Did the import documentation include your VAT registration number? I.e. did the supplier have your VAT reg number when completing the order and shipping info? If not, then you probably won't be able to claim. If it's on there, then you should be able to do it. My recent imports have all asked for VAT number at the time of ordering. HMRC rules here: https://www.gov.uk/guidance/check-when-you-can-account-for-import-vat-on-your-vat-return

Somewhere I have a paper on this, looking at cycling/running time intervals and determining the overallimpact on efficiency. It was certainly not a binary answer. My initial search can't find the paper so I don't know whether I actually saved it, unfortunately.

I buy from Rejs Ltd - https://www.rejsltd.co.uk/drawer-runners they sell some heavy duty runners up to 100kg.

I've used heat engineer in one project and won't use again. The calcs were fine but I put in the data for a completely new installation I was quoting for. Left it a week or two while the customer was mulling it all over and when i went back in to update it all, my whole project had dissappeared from my dashboard and couldn't retrieve it anywhere. Plus I had numerous problems using it with Safari so had to install Chrome. I've just created my own calculator now.

Design and install myself including welding up the manifolds. Ironically, I've trained and become Gas Safe registered since doing it! Yes, pressure test. There are some fairly cheap pressure testers you can get off ebay for one off use.

IMHO the best place to start with system design is with the industry manual: Domestic Heating Design Guide - Everything is in there with regards to heat loss calculation (although the BH community tend to use the calculator designed by Jeremy - you'll find a link to it on the forum), pipe sizing and emitter sizing. For manifolds specifically, I've found scant info on the design but made my own using the the above linked design guide to size all the primary and secondary pipework sizing. Works all fine. My manifolds were copper, soldered with full bore level valves on flow and return to each rad. As already mentioned, you'll need 2 zones but that's pretty simple in the grand scheme of things. One thing not covered in the design guide however is priority hot water setup (sometimes referred to as X-plan) with the heating system which is more efficient than your typical S or Y plan. Select your boiler on its ability to support different DHW and CH temp outputs, its modulation and likewise compatible controls that will modulate boiler output.

Often frowned upon by the old school boys, but mightily handy when you're in a tight spot is the good old friend, Macalpine and his flexible waste connectors. Maybe can help in this instance: https://mcalpineplumbing.com/plastic-chrome-fittings/flexible-fittings-non-return-valves/flexcon5c-flexible-fitting-universal-x-plain-spigot

Thanks all, that was my first port of call. Unfortunately I'm finding the same difficulty getting hold of PAR in the dimensions I want. I've build the door openings for 32mm linings, assuming finished nonimal 27-28mm, but nobody locally stocks or supplies any 32 x in widths greater than 138mm so about 132mm finished. One merchant does list 32 x up to 225 but no stock. Other than that, I've got to go to 38mm so 32mm finished which means trimming the doors which have all been supplied pre finished. Oh, actually, I may have just found some with 32 x 150 so possibly okay for most walls. I just wonder whether this will work okay with shadow gap beads. Then need to find something for the walls with 140mm cls.

I wonder whether I've made a bit of a mistake in my planning. In the designs we've gone for metric doors and the bigger ones too. 826 x 2040 and some 926 x 2040. Fine for the doors eventually as I've found availability a problem for a while. Now I'm struggling with door liners - lots available off the shelf with trenched headers for the smaller doors and untrenched for imperial door widths, but few and far between for the metric liners. The other thing I've found is that the liners are often not wide enough to deal with the full width of my stud walls which use double plasterboard each side, so with stud, PB and skim, none of the standard dimensions work out. I'd like to use 32mm thick door liners, so finished size of ca. 27-28mm but unless I pay silly money - e.g. £80 per liner, it doesn't seem practical. My thoughts now are to getting some 25mm MR MDF ripped to size instead. Any other thoughts or suggestions? (other than plan better in the future 😁)

I just thought I'd add to this one as I just came across Robin Clevett's (from Skill Builder and his own Youtube channel) new hinge jig at https://www.robc.co.uk/shop/ Looks very neat as it doesn't use router bushings but a router cutter. No jig for the door lock yet mind you.

Have you done it yourself? I'd be interested to know any experience of the BCO process of this

I know it well, I'm in the trade too nowadays hence my reference to treating customers. You could very well be right on that.