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- 10 Feb 2025
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Hi all,
I've just moved into a new house and I'm looking for some clarification on how my hot water system works.
I'll explain how I THINK it works, and hopefully someone here can maybe clarify if I'm a million miles out, partially wrong, or somehow correct. It all kind of stems down to a mixture of how does this system work, and is this set up really inefficiently?
There is what I assume to be your standard Worcester Bosch boiler upstairs in the cupboard. It's a Greenstar 24Ri ErP... whatever that means.
This directly does the central heating for the house, and indirectly does the hot water (more on that later).
It's controlled by a Honeywell ST9400C, which is connected to a thermostat in the hallway downstairs. I've programmed this to trigger the central heating at set times of day and turn off and other times, but it's also reliant on the temperature to be below that on the thermostat. So if I turn the thermostat down and forget about it, the next morning the house is going to be cold because I forgot to turn the damn thing up before I went to bed.
I've also programmed this to do the hot water at different times of day, but to be quite frank I have no idea if it's even doing anything with that because of the way the hot water system appears to work.
So, about that hot water system. In the spare bedroom cupboard (whatever genius chose that location needs a good slap), there is what I originally assumed to be the hot water storage tank of the "standard" type. As in the water in the tank is the water that I'm using to fill the sink, shower etc. After moving in however, I found out it's actually a Pandora Heat Bank, a thermal store , details of which are located here https://www.heatweb.co.uk/w/images/e/e0/DS-20_Pandora_Indirect.pdf
Now from what I've read it says that when I use the central heating, it also heats the water up in this thermal store. Okay fine, killing two birds with one stone, that makes sense. The store then has a heat exchanger so when I want to use the shower the mains water comes through, gets heated up by the stored hot water on the other side of the heat exchanger, and I get a really nice powerful mains water pressure hot water shower, that if I so decided I could actually drink. All this works and I must say the water pressure is great and the wife likes the fact the bath fills up quick.
The confusion/problem comes from the fact this thermal store has a 3kW immersion heater on it as well. After moving in I kept hearing this damn tank doing something and it's pretty loud if you are in the room when it does. I originally thought it might be a pump just recirculating the water inside the tank, but based on the fact my electricity usage suddenly goes up by 3kW, I think it's safe to say it's the immersion heater kicking in. I kept an ear out for it today whilst in my office in the next room and it kicked in roughly every 30 minutes for 3-5 minutes. Middle of the day, central heating not on. So what the hell is this actually doing? Is it trying to keep the water in the tank above a minimum temperature? By my calculations, this thing kicking in roughly 48 times a day, for 3-5 minutes at a time, is going to cost me £2.60 a day, or £950 a year. It even seems to come on when the central heating is already on!
So my questions...
-Why does the 3kW immersion heater need to come on if the tank is being heated by the boiler?!
-Come summer does that mean all my hot water is going to be supplied by a 3kW immersion heater because the boiler never comes on for the central heating?
-Why am I setting the Honeywell control system up for "hot water" times if the tank just stays the same temperature all day and night? Is that just a redundant part of the controller because it's based on a different type of system? Because as far as I can tell, the boiler never kicks in just to heat the water in the tank, it only comes on to do the central heating.
-There is a temperature gauge on the tank which seems to be a steady 75'C, but there is also a dial thermostat on the tank that's at 65'C. Is that tank temp vs outlet temp? Is that temperature too high and should be turned down?
Any information or recommendations on how this system works, how to set it up for efficiency etc are much appreciated.
I've just moved into a new house and I'm looking for some clarification on how my hot water system works.
I'll explain how I THINK it works, and hopefully someone here can maybe clarify if I'm a million miles out, partially wrong, or somehow correct. It all kind of stems down to a mixture of how does this system work, and is this set up really inefficiently?
There is what I assume to be your standard Worcester Bosch boiler upstairs in the cupboard. It's a Greenstar 24Ri ErP... whatever that means.
This directly does the central heating for the house, and indirectly does the hot water (more on that later).
It's controlled by a Honeywell ST9400C, which is connected to a thermostat in the hallway downstairs. I've programmed this to trigger the central heating at set times of day and turn off and other times, but it's also reliant on the temperature to be below that on the thermostat. So if I turn the thermostat down and forget about it, the next morning the house is going to be cold because I forgot to turn the damn thing up before I went to bed.
I've also programmed this to do the hot water at different times of day, but to be quite frank I have no idea if it's even doing anything with that because of the way the hot water system appears to work.
So, about that hot water system. In the spare bedroom cupboard (whatever genius chose that location needs a good slap), there is what I originally assumed to be the hot water storage tank of the "standard" type. As in the water in the tank is the water that I'm using to fill the sink, shower etc. After moving in however, I found out it's actually a Pandora Heat Bank, a thermal store , details of which are located here https://www.heatweb.co.uk/w/images/e/e0/DS-20_Pandora_Indirect.pdf
Now from what I've read it says that when I use the central heating, it also heats the water up in this thermal store. Okay fine, killing two birds with one stone, that makes sense. The store then has a heat exchanger so when I want to use the shower the mains water comes through, gets heated up by the stored hot water on the other side of the heat exchanger, and I get a really nice powerful mains water pressure hot water shower, that if I so decided I could actually drink. All this works and I must say the water pressure is great and the wife likes the fact the bath fills up quick.
The confusion/problem comes from the fact this thermal store has a 3kW immersion heater on it as well. After moving in I kept hearing this damn tank doing something and it's pretty loud if you are in the room when it does. I originally thought it might be a pump just recirculating the water inside the tank, but based on the fact my electricity usage suddenly goes up by 3kW, I think it's safe to say it's the immersion heater kicking in. I kept an ear out for it today whilst in my office in the next room and it kicked in roughly every 30 minutes for 3-5 minutes. Middle of the day, central heating not on. So what the hell is this actually doing? Is it trying to keep the water in the tank above a minimum temperature? By my calculations, this thing kicking in roughly 48 times a day, for 3-5 minutes at a time, is going to cost me £2.60 a day, or £950 a year. It even seems to come on when the central heating is already on!
So my questions...
-Why does the 3kW immersion heater need to come on if the tank is being heated by the boiler?!
-Come summer does that mean all my hot water is going to be supplied by a 3kW immersion heater because the boiler never comes on for the central heating?
-Why am I setting the Honeywell control system up for "hot water" times if the tank just stays the same temperature all day and night? Is that just a redundant part of the controller because it's based on a different type of system? Because as far as I can tell, the boiler never kicks in just to heat the water in the tank, it only comes on to do the central heating.
-There is a temperature gauge on the tank which seems to be a steady 75'C, but there is also a dial thermostat on the tank that's at 65'C. Is that tank temp vs outlet temp? Is that temperature too high and should be turned down?
Any information or recommendations on how this system works, how to set it up for efficiency etc are much appreciated.
