Any ideas on this hot water problem?

Muahahaha

I set my hot water to heat from 7am-8am to take advantage of the night rates. But I dont have a shower till about 1pm. Most of the time thats fine but perhaps 20% of the time the water from the shower is not hot enough, barely luke warm just 5 hours after heating it. I checked the usage on my smart meter data and it defintely is heating it as I see it used almost 4kw between 7 and 8am. I cant work why it is doing this and the only thing I can think of is on colder mornings the hot water tank cannot hold the hot water for 5 hours and it decreases in temperature to below luke warm in those 5 hours sitting in the tank. Is this a possibility or could there be a different problem where the immersion is using the electricity but not actually heating the water that much?

The other question is when this happens I put on the boost function for 30 minutes so Ive enough hot water for a shower, it is an E7 Horstmann. Ive noticed that just uses 1.2kw to heat it for 30 minutes on the boost function. Im wondering is there any reason not to just use the boost function every day for 30 minutes instead of the main tank heater? Even on the day unit rates it would work out cheaper (1.2kwx2 vs 4kw). Any reason not to do it this way? Ive a smart interface and app on the E7 Horstmann so could set it to come on for 30 minutes boost every day just before I take a shower about 1pm, I dont have to manually press the button to get it to start heating.

Muas Tenek

If it is losing heat faster on cold mornings it is quite possibly due to the Mpemba Effect.

https://www.youtube.com/watch?v=7rmaGGxcBHg

Lenar3556

https://www.boards.ie/discussion/2058403849/any-ideas-on-this-hot-water-problem

Difficult to say without examining the setup in detail, but as a best guess;

If 4 KW/h of electricity has been consumed by the immersion then this has without doubt gone into heating the water.

It is likely that the primary element (used from 7am to 8am) is longer and heating a larger volume of water than your ‘boost’ element which is heating a smaller volume of water at the top of the cylinder and as a result can get it hotter faster.

Colder weather may well play a factor, perhaps in terms of the cylinder retaining its heat, but more significantly the water feeding the cylinder will be colder to begin with, so the immersion has more work to do.

In summary, I think the 1 hour heating time is a little skimpy and you would need to increase this somewhat if you need a full cylinder of hot water. Alternatively if the boost element is generating enough hot water for your needs in 30 minutes, this seems like a good solution. Note however that this 30 minute boost will have benefited from the partially heated water from the morning.

Is the cylinder well insulated?

John.G

Its more than likely that those elements are not more than 3kw, if your immersion is of the top mounted dual element type then the boost (sink) element will be heating ~ 30L, so, at a cut of 60C then it will raise the (30L) from a minimum of say 25C to 60C (requires 1.22kWh) in 24/25 minutes, say 1/2 a hour. don't know what the capacity of the cylinder is or the length of the bath element but assuming a average 30" then will increase the ~ 80L by 32C in a hour (3kWh) so maybe a final temperature of 45/47C assuming a average starting temp of 15C. The big problem with the dual element immersion is that there is only one thermostat which only extends the length of the shorter sink element so the only way to guarantee a fully reheated 80L or whatever is to start from a almost fully cold/cool cylinder, for example if you were to heat 30L with the short element and then switch over to the long element then nothing will happen as the stat is still satisfied so heated vol will vary with the long element depending on the cylinder temperatures.

You did say the cylinder is apparently heating for a full one hour period so would expect the temperature to be ~ 45/47C (thats assuming a dual element immersion), if the cheap rate applies before 0700 then maybe increase the time to 2hours, 0600/0800, the consumption should still only be 4.2kWh and the immersion should switch off at 60C after 1h 25m, say 1 1/2 hours.

Muahahaha

@Lenar3556 and @John.G thanks so much for the detailed explanations, Im a lot clearer now on whats being going on as I didnt know about the variables of the different immersions heating different volumes of water.

Just on my suspicion that it could be linked to very cold mornings I went up to the cold water tank in the attic last night and that is not insulated, either the tank or the pipework coming from it. It doesnt have a cover either and the water inside was cold, like really, really cold. It felt like 5 degrees on my hand even while the ambient air temperature felt noticeably warmer. So I think I need to get that tank insulated so the water going in to heating in the hot water cylinder isnt as cold.

I think going forward I'll just heat it on boost on the day rates as all I need is one 6 minute shower and a bit of hot water at the sink so that should cover it. I can do that by using just 2.4kw on a 30 minute boost on day unit rates rather than almost 7kw (over two hours) on night unit rates. As said 1 hour heating a larger volume of water wont cut the mustard but I dont need such a volume of water so better to heat the smaller amount using the boost function.

Just on my cylinder I dont know how old it is and cant see a brand name on it, looking at Screwfix it might be the Joule brand? The house was built 1996 and Im only here since 2017. The cylinder is insulated but Im not sure how well, Id guess it is at least 15 years old but maybe 20+. Have hot water cylinders improved a lot since then in terms of better insulation and might it be worth looking at replacing it to save on energy

John.G

Thats a A rated energy cylinder (top class) and you can see the daily heat loss in kWh, on the label, the cylinder capacity should also be stamped somewhere so very easy then to calculate the temperature drop. You might also see the immersion element power, kW, on each element, post them as well if you like, can then see exactly what a 30min boost is inputting to the cylinder in kWh, likewise with the bottom element. These two elements, unlike the dual element immersion type, will have their own separate cylinder stats.

whizbang

Is that pipe on the right buried into the wall?

You should have 19mm insulation on all the pipwork coming out of the top of the cylinder.

What kind of heating do you have? If theres a heatine loop in the tank its going to pull some heat out also.

dathi

as whizbang says all pipe work should be insulated taken from partL of building regulations Tgds.

2.2.4.4 The hot pipes connected to hot water storage vessels, including the vent pipe and the primary flow and return to the heat exchanger, where fitted, should be insulated to the standard outlined in paragraph 2.2.4.3above, for at least one metre from their point of connection.

Muahahaha

https://www.boards.ie/discussion/comment/123298669#Comment_123298669

thanks for this, I'll buy some 19mm insulation over the weekend and sort this aspect to 1 meter up the pipes as per Part L as @dathi above said.

The pipe on the right isnt buried in the concrete wall per se, the channel it is inside is 75mm of insulating board on the inside of a gable wall. It was the only way to install it without removing all pipework and reducing the width of the understairs room to the point the washing machine it also hosts would have been too tight.

My understanding of a heating loop is a pipe going to a back boiler or similar, I dont have one of them, the heating of the hot water is electric only ran by a H7 Horstmann which I recently upgraded to smart controls with this product

https://www.expertelectrical.co.uk/horstmann-smart-immersion-heater-control

John.G

Can you post a photo of the energy label and any info you can see re cylinder capacity.