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Hopefully a quick question. Background installing an unvented cylinder. Location is remote from the cold water manifold, preventing connection of the balanced port to the cold supply. House already has a PRV just after the stop cock set at 2.5 bar. Cylinder comes with a combined inlet set, set at 3 bar. Can I just blank the balanced line off? Do I need the second PRV to comply with regs?

Hi All, The plumbers put in our UVC cylinder yesterday. I have raised a few things I spotted with the main contractor and he was getting in contact with the plumber. Could those of you with more experienced eyes please have a glance at my picture and let me know anything else that needs to be rectified. What I've noticed/questioned. 1. There is no tundish fitted and the over temp valve discharges via some 16mm pipework over a long distance to a hidden pipe into the main waste water system. 2. Does the tank require an overpressure valve on the cold feed? There is one on the cold main entering the house. 3. Does the tank require a thermostatic mixing valve? 4. Is it safe to have a switchable valve on the expansion vessel? Thanks in advance.

I have recently moved to an old stone walled cottage that was converted to a bungalow in the 70s. It has a 4kWp PV system and a 1.4kWp ST system with an oil fired boiler for CH and DHW. There is a 230l cold water tank in the loft and a 140l vented hot water tank. I shall continue to use the oil fired boiler and would like to have mains pressure hot water. The ST system is a Genersys 1200 with DC12 controller which was installed in 2009 and seems to be working well. I am trying to decide whether to keep the ST system and use a ~250l twin coil TS such as a Grant DuoWave TS or use a twin coil UVC. I looked at the Harlequin Heatstream Plus but it only has one heating coil so would mean using the PV to heat the water with the immersion. I had a UVC system in my last house which worked well but it would require annual maintenance. The alternative would be to remove the ST and use an external oil fired combi boiler. I have discounted Sunamps etc. Any ideas would be helpful.

Apologies if this has been asked before and if it's in the wrong category, but our M+E consultant is recommending a Vaillant ASHP which I'm fine with but when I look at the Vaillant UVCs, I'm concerned that they won't get the best out of the solar PV diversion. Most solar PV diverters have two outputs, so that once the first output has stopped accepting energy the second output is activated. So if you are doing what most people do, diverting to an immersion in the UVC for hot water, you'd ideally want to have 2 immersion heaters in the UVC, so 1st heat the top of the tank, then when that's hot start to heat the bottom of the tank. The Vaillant UVC has one immersion in the middle of the tank - so only the top half would benefit from the solar diversion. An alternative would be say the Gledhill StainlessLite Heat Pump cylinder but that only has a single immersion heater point which is at the bottom - theoretically better because on a good day you could heat all the tank but not on a marginal day as you'd only warm the whole tank up a bit. Anyone know of a cylinder suitable for ASHPs with 2 immersions - middle and bottom? Thanks in advance for any help. Simon

I am in the process of designing (with architects!) and commissioning a small low-energy house which will rely mainly on solar pv for energy. There is no gas at the property. I have over 15 years experience of solar thermal and solar pv. My current house uses solar pv exclusively for hot water for more than 7 months per year, uses gas for ch & backup hw for colder months. My current 3 immersion design cylinder has proved very effective. I have trawled through various heating and dhw designs including thermal stores and multi-tank solutions but cannot reconcile the different requirements (eg thermal stores need a good temperature gradient to provide dhw - heat pumps provide 55º as a working maximum). I have also noted comments on this forum. (“Hot water and heating are different – keep them separate!”) However I’m still looking for an efficient & effective solution. I am considering using a large unvented cylinder (say 500 litres) which will also act as a buffer for a heat pump and a thermal store for underfloor heating. For at least 8 months of the year the total input would be from solar pv through immersion heaters. For the colder months there would be the possibility of input from a heat pump. Primary heating would be through 3 immersion heaters. I have included a diagram. I see the following as advantages : 1. A single tank with straight-forward plumbing. No complex valves or diversions. 2. Separation of circuits for input/output. Antifreeze needed only in the heat pump circuit. - Better heat transfer to UFH with water than with antifreeze mixture. (and much less of it) 3. Ability to maximise use of solar pv (8kW) throughout the year. 4. Possibility of running as a fully electric system without heat pump - under consideration for at least one year to assess relative costs. Also provides alternative heating if heat pump fails. 5. Typically : we boost heat in the mornings (before 9.00) and in the late afternoon/early evening. Background temperature maintained at other times (although with a good store in the slab this will become less pronounced). Best efficiency from an ASHP will be when the outside temperature is highest and the best use of solar pv will be between 9.00 and 17.00. So having a facility to store heat at these times will maximise both efficiencies. I recognise one potential problem: In our current location, with excessive water hardness, cylinders frequently deposit more than 0.5kg calcium salts per year. We have completely avoided this by quality water softening and would do so in the new location. Although the physical design is simple the efficiency will depend on the control circuits. I propose to design & program these myself rather than rely on the current commercial provisions which seem to be over-complicated but still limit options to those provided by manufacturers. All of the plumbing would be installed by G3 qualified tradespeople. So I would welcome constructive guidance … 1. Is there any commercial system which already follows these lines which I’ve missed? 2. Has anyone on this forum taken a similar line – with what results? 3. Are there any genuine down-sides which I’ve missed?

Hi, Anyone any experience of WH UVC. Plumber is proposing 400 or 500 litre to be heated by Daikin ASHP. My house is eventually being completed after a lot of remedial work. Thanks

Grateful for advice on the following. I'm doing a self build in the Stirling area. Its a five bed property (180m2 in total) with ufh downstairs (120m2) including three bedrooms downstairs and two bedrooms upstairs with rads. One bathroom and three en-suites in total. I was hoping for some advice on boiler and UVC sizing? We will be required to install PVs so I'm also wondering what issues to consider in terms of integrating it with the heating system/hot water? Looking for the most cost effective option. I did consider ASHP but have decided to opt for LPG and PVs. Any pointers much appreciated.

Excerpt from a previous thread. A member asked..... I am looking at an HTG thermal store for a DHW & Heating upgrade, I will be using a gas boiler heating the TS only, together with PV and immersion heater. The TS comes with a solar thermal coil fitted as standard. The gas boiler would normally be connected directly to the TS but I was wondering if I could use this solar coil for the system boiler to obtain some fluid separation ? The size of our home with # of radiators/bathrooms etc. would suggest I need a TS of around 300 litres but if I view the store as a battery should I install a larger store say 400 / 500 ltrs to help with the gaps in PV availability ? I guess there is a risk of oversizing as the volume should be within the capabilities of the immersion / gas boiler to recharge it ~ any thoughts or advice would be welcome. The TS is presently required for 12 radiators, 2 bathrooms & DHW, I am hoping to take advantage of my PV power hence the TS otherwise a fair size combo probably would have been the way to go. I am also building extra ground floor space so I also have been considering UFH but from your previous advice I am going to need more insulation to even consider going down this road. I have a beam & block floor with only 40mm poly then wyroc so not good, I am able to put 75mm underneath the floor between the beams which would help ~ but still not sufficient although if I am using this space underneath the ground floor as a store should I be too concerned. I have had experience with TS excessive heat in a flat some years ago, it was located in the centre of the flat off the hallway and I did ask engineers how to reduce the heat output but they looked blank at me. The small gas boiler was set at max heat output for efficiency as per the operating instructions but after not getting any useful help from heating guys, I had to turn the boiler down to half heat which totally made our lives much better, so JSH I appreciate this problem..... I presently have a traditional copper tank upstairs about 110 ltrs and is generally heated by the PV system and overall meets our requirements as there is only two of us. I am considering putting the TS in the utility room and using the heat to make a drying room etc. The TS is stainless steel and comes pre plumbed with a high efficient external heat exchanger (46lts per min, we have high water pressure) I could also add to this TS a similar external heat exchanger for UFH so it would give me scope for going the UFH direction. The additional copper header tank can be installed above the TS , is there any requirement for this to be higher than the radiators in the bedrooms or will it be ok ?