Question Posted October 1, 2022 Share Posted October 1, 2022 Is it an unusual to take two and half hours for our new 250 litres unvented cylinder to heat up the water from cold to 60 C? (I have seen figures of half an hour on the internet). The boiler is a 30Kw Worcester Bosch. The unvented cylinder is a twin coil solar system. We got that to future proof, but we don't have solar panels. We may get panels in the future. Telford Tempest 250 Litre Twin Coil Solar Indirect Unvented Cylinder - Cylinders2Go The boiler is connected to the bottom coil only. Nothing is connected to the other coil. The coil outlet/boiler return from the cylinder is still very hot. I wondered whether the hot water is going through a short coil and therefore not heating the water that much. Is this a more expensive way of heating water? Link to comment Share on other sites More sharing options...
SteamyTea Posted October 1, 2022 Share Posted October 1, 2022 It is about 16 kWh of storage, so at 30 kW input, half an hour seems reasonable (add a bit as the hotter the cylinder is the greater the losses and the harder it gets to raise it an extra degree. So something seems wrong. 1 Link to comment Share on other sites More sharing options...
Miek Posted October 1, 2022 Share Posted October 1, 2022 The solar coil at the bottom of the tank should have a kW rating, check on the cylinder. Usually the solar coil is quite efficient at heat transfer as its designed for a temperature difference across the coil of around 4 degrees C and so they are often quite a long coil. Link to comment Share on other sites More sharing options...
Question Posted October 1, 2022 Author Share Posted October 1, 2022 (edited) I can't see KW rating for the solar coil at the bottom. I can find it for other manufacturers online but not for Telford cylinders. I see that if the KW rating is high, the recovery time is quick. So, thanks for pointing this out to me. I'll try to speak to the manufacturer's tomorrow. Edited October 1, 2022 by Question Link to comment Share on other sites More sharing options...
ProDave Posted October 1, 2022 Share Posted October 1, 2022 What is the flow temperature from your boiler? Link to comment Share on other sites More sharing options...
Question Posted October 1, 2022 Author Share Posted October 1, 2022 (edited) ProDave, the commissioning checklist was completed by the plumber and it says What is the maximum hot water flow rate at set thermostat (measured at high flow outlet)? 14 l/min (Hot water thermostat was set at 60 C) Edited October 1, 2022 by Question Link to comment Share on other sites More sharing options...
Question Posted October 1, 2022 Author Share Posted October 1, 2022 ProDave, sorry I misunderstood your question. We recently had the boiler moved but he did not do any commissioning document. We have the original one when it was first installed in 2016. It says Central Heating flow temperature of 68 C and 47 C return temperature. I can't find any flow temperature for the hot water. Link to comment Share on other sites More sharing options...
JohnMo Posted October 1, 2022 Share Posted October 1, 2022 It could the margin between the flow from the boiler and thermostat setting, which is different with different coil sizes. A small capacity coil needs a bigger margin between boiler flow temp and thermostat set point, otherwise what happens, boiler heats the cylinder up to about 50-55 degrees, the shuts down on return temp being high. The boiler then stops and starts while it forces the temp up. This is basically short cycling, using loads of gas/oil. To fix increase the flow temp another 5 degs or so. The manual say ensure boiler is set to 75 deg. Telford-Cylinder-Installation-Guide.pdf Link to comment Share on other sites More sharing options...
Nickfromwales Posted October 1, 2022 Share Posted October 1, 2022 5 hours ago, Question said: ProDave, sorry I misunderstood your question. We recently had the boiler moved but he did not do any commissioning document. We have the original one when it was first installed in 2016. It says Central Heating flow temperature of 68 C and 47 C return temperature. I can't find any flow temperature for the hot water. Interrupting the gas supply means a new gas cert MUST be issued!! An appliance moved today should have a printed CO2 PPM ticket from the flue gas analyser to prove it’s burning clean and efficiently. Ask why this has not been done. What they wrote back in the day would have been rehearsed and not measured btw Standard practice back then sadly. Why is this boiler connected to the solar coil?? That is a direct deviation from the MI’s ( manufacturers installation instructions ). The solar coil, drum roll please, is for the solar to be connected to!! That’s why the recovery time is so huge, you’re heating via the wrong coil What is connected to the boiler coil? Get this is changed and then you’ll see the difference. The info you quote for 30 mins reheat ( recovery ) time will not be by anyone using the wrong coil. You also need to check that the flow temp is high enough to comply with he MI’s. Sounds like your plumber is of questionable pedigree if they’ve left this install this way and not done you a new gas cert. BTW, you’re probably not currently insured with your building insurance if this is not in your possession. Link to comment Share on other sites More sharing options...
Question Posted October 3, 2022 Author Share Posted October 3, 2022 Thanks Nick. I haven't been clear. I did get a Gas Safe certificate for the recent installation. I understood a commissioning document is something different. When the boiler was first installed in 2016, the engineer filled in and signed a gas boiler system commissioning checklist in the manufacturer's "installation, commissioning and servicing instructions" booklet. The 2016 commissioning checklist contains some information about the boiler like CO levels. In May 2022, the engineer has not provided me with a commissioning document for the boiler (but did do one for unvented cylinder). There is no information about the C0 or CO2 levels when he moved the boiler. There is no sticker on it. According to the unvented cylinder commissioning document, the maximum primary flow temperature is 75 C. In 2016, the engineer who installed the boiler did not produce a Gas Safe certificate (and there is no record on Gas Safe), and he crossed out the section "domestic hot water Mode" in the commissioning checklist. At the time, we just trusted tradesmen to do the right paperwork. I will contact the unvented manufacturer and ask them which coil I should be using. I say that it takes a long time to reach the right temperature, because the boiler remains on continuously for at least 2.5 hours. Is that a correct conclusion? I am still on a journey on learning about heating, electricity, plumbing etc, so apologies if I am not clear. We found with some workmen, even the qualified ones, that we rapidly find out things that they should know but which they don't. It really is appalling. 1 Link to comment Share on other sites More sharing options...
Temp Posted October 3, 2022 Share Posted October 3, 2022 2 hours ago, Question said: I say that it takes a long time to reach the right temperature, because the boiler remains on continuously for at least 2.5 hours. Is that a correct conclusion? As @SteamyTea said the maths suggests more like 30-45 mins to go from 10C to 60C. The boiler will remain "ON" as long as the tank calls for heat (eg thermostat not satisfied). If the tank coil is too small then the return temperature will rise too much and that increases the flow temperature. At some limit, and depending on the type of boiler (gas vs oil) the boiler either modulates the flame down (so it produces less than 30kW) or cycles on and off (so the average is less than 30kW). Link to comment Share on other sites More sharing options...
Radian Posted October 3, 2022 Share Posted October 3, 2022 On 01/10/2022 at 15:44, Question said: The boiler is connected to the bottom coil only. Nothing is connected to the other coil. That's the solar coil right? Why did your plumber connect the boiler to that? Link to comment Share on other sites More sharing options...
Question Posted October 3, 2022 Author Share Posted October 3, 2022 I'll speak to the manufacturers about the boiler connections to the cylinder. See what they say. I'll post here what they say. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now