Hi this is a great website - I have a question i'd like help with please if possible?
I am moving next month (april) and apparantly the house has a thermal store. I have never had one of these before, only had a combi boiler or a hot water tank in my old home years ago. My question is - what's the difference, and can I use it the same? I'd like to know a bit about i before moving in. I have tried to look for info on the web about it but am not sure where to look too be honest. Does it supply hot water the same as a normal hot water tank?
Having lived with both, you'll be aware of the limitations of a combi - personally I think they are the work of the devil and the only valid reason for fitting one is because the developer was too incompetent to find room for a small tank. But that's just my opinion.
In a thermal store, the cylinder is unpressurised (normally open vented) and contains hot water heated by whatever means are installed. They are really great for combining multiple heat sources such as a back boiler/wood burning stove and or solar in addition to a boiler. The DHW is passed through a coil inside the tank, and so the water heats up by conduction through the walls of the coil. The coil can easily be made to take mains pressure, and so the DHW is generally fed direct from the mains (with a pressure reducing valve if required). So you get mains pressure hot water (like the combi), but without the reliability problems a combi can bring to the party. Depending on the size and design of the store, plus the temperature it's run at, flow rates should be better than a combi. The DHW is passively heated - it will work with the mains off using the stored heat.
A heat bank is very similar, but generally uses a plate heat exchanger external to the store - these usually have very much higher flow rates for DHW. These need a pump to pump the hot water round the heat exchanger and store - so you lose the hot water with the power off.
In both cases, if it wasn't clear from the description, the water in the store does NOT come out of the hot water tap.
In many cases, the central heating will also run from the store. This decouples the CH flow rate from the boiler flow rate - and so it's possible to fit a system with TRVs on all rads a modulating pump. That works very nicely with each room temp set by the TRV instead of having a central thermostat.
If done nicely, there'll be an immersion heater that can run the central heating as well as the hot water - so not need to freeze when the boiler breaks down
I recently fitted a thermal store in my flat, and wrote it up on the
Navitron forums. There's a diagram of the system part way down the first page which may help you visualise the sort of system you may come across.
BTW - is this your house or rented ? If it's rented then you get no say, but if it's yours then beware of plumbers who take one look at the store and after a sharp "sucking through teeth" tell you that it's rubbish and you need to replace it with a combi. In such a situation, the best thing to tell them is the way out and don't let the door hit them on the way out.
