Diablo Posted November 21, 2017 Share Posted November 21, 2017 Guys, I live in a new build bungalow with an oil boiler which fires the UFH system and 300L unvented HW cylinder. This is our first winter here and I have noticed a few issues with the heating/hot water system: Q. When the UHF comes on at the same time as the HW, it seems to starve the supply to the HW circuit as I frequently end up having luke warm showers. Is there any way of ensuring the cylinder gets sufficient supply? Q. The other thing I have noticed is that there can be warm water in the tank, but unless I switch on the secondary hot water circulation pump, we do not get hot water to the bathrooms. The furthest bathroom is about a 20m horizontal run from the tank. I am loathed to keep the pump for any long periods of time, as it would mean that hot water is being pumped around a cold loft space. Does anybody know what is causing this and how to get around it? Any thoughts or advice would be gladly received. All the best, Rog Link to comment Share on other sites More sharing options...
le-cerveau Posted November 21, 2017 Share Posted November 21, 2017 All sounds strange. DHW should come from the tank so if you have lukewarm showers then the tank was not hot and it sounds like it cools down overnight (what a surprise) and whilst the UFH is on doesn't heat up very quickly. (Solution heat it up in time for your shower). The circulation pump should have no impact on your ability to get hot water, just the time you wait for it! It should pull the return leg back to the center of the DHW tank, whilst the DHW feed should be from the top of the tank (is it all put together properly?). As you have a circulation system the pipes should all be very heavily insulated to reduce losses (shock/horror is the builder skimped on pipe insulation. We would need to see a system layout to provide proper advise then our resident plumbing expert could comment properly. Link to comment Share on other sites More sharing options...
PeterW Posted November 21, 2017 Share Posted November 21, 2017 Is it a UVC or is it a Thermal Store ..?? There may be no zone valve stopping the flow through the cylinder so when the UFH comes on it may be drawing cold water back through the UVC coil. Got any photos ..?? Link to comment Share on other sites More sharing options...
Diablo Posted November 21, 2017 Author Share Posted November 21, 2017 Link to comment Share on other sites More sharing options...
Diablo Posted November 21, 2017 Author Share Posted November 21, 2017 10 hours ago, le-cerveau said: All sounds strange. DHW should come from the tank so if you have lukewarm showers then the tank was not hot and it sounds like it cools down overnight (what a surprise) and whilst the UFH is on doesn't heat up very quickly. (Solution heat it up in time for your shower). The circulation pump should have no impact on your ability to get hot water, just the time you wait for it! It should pull the return leg back to the center of the DHW tank, whilst the DHW feed should be from the top of the tank (is it all put together properly?). As you have a circulation system the pipes should all be very heavily insulated to reduce losses (shock/horror is the builder skimped on pipe insulation. We would need to see a system layout to provide proper advise then our resident plumbing expert could comment properly. Hello, the DHW does indeed feed from the top of the tank and returns closer to the bottom (Main 300 UVC). In our case, the circulator pump definitely seems to help draw the water out of the cylinder. If I switch on the shower at a given temperature setting but at e.g. 50%, I might not get hot very hot water. If I open the shower tap fully (leaving the temperature unchanged) it does appear to get warmer. Other times, the water will cool down in the middle of a shower, but I have found that switching on the circulator pump seems to help. Again, it sounds as the system is struggling to get the hot water out of the (bottom?) of the tank. Thanks again. Link to comment Share on other sites More sharing options...
Diablo Posted November 21, 2017 Author Share Posted November 21, 2017 10 hours ago, PeterW said: Is it a UVC or is it a Thermal Store ..?? There may be no zone valve stopping the flow through the cylinder so when the UFH comes on it may be drawing cold water back through the UVC coil. Got any photos ..?? Hi, It is a UVC. The three zone valves (2 for UFH and the other for DHW) are on the flow pipe coming off the boiler. Let me know if you need any more pics (hopefully you don't need any of me in the shower ) Let me know if you want me to post any other pics. Link to comment Share on other sites More sharing options...
PeterW Posted November 21, 2017 Share Posted November 21, 2017 Close the isolator above that circulation pump and see if it makes a difference..... There is a non return valve in that lot and it looks like it’s in the wrong place... 1 Link to comment Share on other sites More sharing options...
Diablo Posted November 21, 2017 Author Share Posted November 21, 2017 24 minutes ago, PeterW said: Close the isolator above that circulation pump and see if it makes a difference..... There is a non return valve in that lot and it looks like it’s in the wrong place... Hi PeterW, Wow...I closed the isolator above the pump and the water in the shower seems much hotter and stayed consistently hot. The HW at the kitchen and laundry taps (much closer to the tank) are also much hotter.... If you get a moment, I would love to hear your thoughts on what is going on??? Can I leave the isolator closed? Meanwhile, thanks so much for your help! Link to comment Share on other sites More sharing options...
ProDave Posted November 21, 2017 Share Posted November 21, 2017 55 minutes ago, Diablo said: Hello, the DHW does indeed feed from the top of the tank and returns closer to the bottom (Main 300 UVC). In our case, the circulator pump definitely seems to help draw the water out of the cylinder. If I switch on the shower at a given temperature setting but at e.g. 50%, I might not get hot very hot water. If I open the shower tap fully (leaving the temperature unchanged) it does appear to get warmer. Other times, the water will cool down in the middle of a shower, but I have found that switching on the circulator pump seems to help. Again, it sounds as the system is struggling to get the hot water out of the (bottom?) of the tank. Thanks again. I suspect you thermostatic shower mixer has failed. This is exactly how ours behaved when it failed. Link to comment Share on other sites More sharing options...
PeterW Posted November 21, 2017 Share Posted November 21, 2017 (edited) 33 minutes ago, Diablo said: Hi PeterW, Wow...I closed the isolator above the pump and the water in the shower seems much hotter and stayed consistently hot. The HW at the kitchen and laundry taps (much closer to the tank) are also much hotter.... If you get a moment, I would love to hear your thoughts on what is going on??? Can I leave the isolator closed? Meanwhile, thanks so much for your help! Right... Edited the image you sent as below : What should be happening is the cold water should follow the blue arrows - through the PRV and then into the bottom of the tank. The circulation pump should pull water from the top of the tank and return it to the bottom, following the red arrow. The issue is where the non-return valve is - indicated by the yellow arrow. What is happening is the pressure is pushing cold water past the pump following the purple arrow, mixing at the shower and basically providing lukewarm water everywhere. When the pump is on, it would provide some resistance to the flow but not much, hence why the shower gets a little warmer. The fix is to add an additional non return valve where the green arrow is, with the flow coming from the pump into the main cold tank feed. The current one would stop backflow into the cold supply, the new one would stop the water pushing past the pump. @Nickfromwales will be along shortly to tell me I'm wrong.... Edited to add that yes, you can leave that valve closed but turn the pump off... it looks like its lost its cover too..?? While you've got the cold water isolated I would replace both the pump and add another NRV.... Edited November 21, 2017 by PeterW Comment re valve Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 22, 2017 Share Posted November 22, 2017 Sorry I'm late @PeterW you get the blue peter badge, but no cigar for not spotting the other side effect here The non return is indeed needed where it is, but for the wrong reason, ( I'll explain below ). Add another, where the green arrow is and your problems will end. The pump ideally wants moving too as it shouldn't be pumping downwards TBH, but instead should be laying horizontal or vertical but travelling upwards to allow natural venting / removal of air. Not life or death but can add to the longevity of the pump. Insulate the pipework in the attic and have that hot return ( HR ) pump triggered by an occupancy switch like this in the bathrooms so it only runs briefly prior to when it's needed. It can be set to run off a timeclock too if easier but I'd certainly not make it redundant as it's there to help, by circulating the dead legs of hot water pipework to massively reduce waiting times at the outlets ( particularly the basin hot taps when washing hands after visiting the loo ). One observation is that the plumber has fed the HR into the very bottom of the tank whereas it should be going into a dedicated tapping midway up the cylinder. Does the cylinder have a blanked off tapping midway up somewhere around its circumference? Not all UVC's have one so that's maybe why it's like this. The problem / side effect here is that a system with a HR pump should only be able to draw hot / very warm water back up the return leg when the pump is off. In this situation the plumber hasn't mitigated against the fact that he's connected it where luke warm / cold water will reside, hence your system is currently able to simultaneously draw cool water and hot water into the hot pipework, hence your problem when the pump is off. Another is that in a house with all UFH this should really have been a thermal store. An hour or so after the heating comes on, go see how often the boiler is lighting and then going off whilst there is demand for heating. It's probably cycling quite a bit then and could benefit from a buffer. All depends if you want to open that can of worms or not as ignorance can be bliss ??. 1 Link to comment Share on other sites More sharing options...
PeterW Posted November 22, 2017 Share Posted November 22, 2017 7 hours ago, Nickfromwales said: One observation is that the plumber has fed the HR into the very bottom of the tank whereas it should be going into a dedicated tapping midway up the cylinder. Does the cylinder have a blanked off tapping [...] I’d noticed that @Nickfromwales but couldn’t see anything on the UVC to allow a return. Concern with the way it is currently, it may cause boiler cycling as it will circulate through the whole tank and not the top Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 22, 2017 Share Posted November 22, 2017 1 hour ago, PeterW said: I’d noticed that @Nickfromwales but couldn’t see anything on the UVC to allow a return. Concern with the way it is currently, it may cause boiler cycling as it will circulate through the whole tank and not the top Yup, but at least they'll always have a tank FULL of hot water . Link to comment Share on other sites More sharing options...
Diablo Posted November 22, 2017 Author Share Posted November 22, 2017 Gents, This is fantastic and your help is hugely appreciated! I have checked the UVC and I cannot see any option to feed the HR higher up. As it happens, I had a plumber booked in for tomorrow morning to do something else, so I will get him to address this issue at the same time. I will report back asap. All the best, R Link to comment Share on other sites More sharing options...
Diablo Posted December 7, 2017 Author Share Posted December 7, 2017 A quick update: The plumber fitted a double check valve below the pump and everyone's happy! Thanks for the help. 1 Link to comment Share on other sites More sharing options...
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