DIY Doctor UK DIY Forums

Hi all, I need help figuring out the central heating/water system in my house. It's a 4-bed, 2 bath, built in 1910.
Downstairs at rear of house we have a combi boiler and expansion tank. Upstairs in an airing cupboard we have a hot water cylinder. In the loft there is a large tank which one plumber told me is not in use since I have a combi boiler.
We have a few ongoing problems but the first one I'm trying to tackle is; whenever we use the hot water continuously - run a bath or fill the sink. A loud vibration can be heard and felt coming from the loft tank or pipework going to/from it. The vibrations travel down to several of the radiators whether they are on or off.
Is it likely the loft tank IS still in use, and would this be hot or cold water? The noise appears to coincide with the hot water cylinder refilling, but sounds like it's coming from the loft tank.
I have a circuit breaker labelled "water heater" which I've had switched off for months now yet we still have hot water so I assume it is not related/defunct.
Anyone got any advice to what could be causing the noise/vibration and also if the loft tank is likely to still be in use and for what purpose? Thanks.

The main advantage of a combi boiler is the hot water is same pressure as cold water, so a thermostatic mixer can power a shower quite well.

Today you can get hot water tanks at mains pressure, however it means they need testing once a year, so to my mind not really a good idea, in the main the tank is a heat exchanger, and you have a coil of pipe inside the tank to transfer the heat, it can work in either direction, so you can have mains pressure water in the hot coil, and a vented tank, but in the main if your water pressure is the same for hot and cold likely it is using the combi boiler for DHW.

The combi boiler normally means no storage tanks, but this means no where to store energy from solar power, so there has been a move back to storage tanks, they also allow multi water heating systems to all run the same central heating.

So you can have solid fuel back boilers, LPG boilers, and electric all running the same CH and DHW.

But it seems more likely some one has not used the combi option on the boiler, and you in fact have a system boiler. Have you googled the info on your boiler to see what you have?