I'm in the UK, we got a new recently due to the rebate recently offered on really old boilers.
If you get a decent boiler it provides savings because it is more efficient. They are called "condensing" combination boilers - the condensing action reclaims lost heat, I think.
We got a Vaillant, who also make the glow-worms. Never heard of Ferroli. And yes we get decent hot water pressure. I would check with a few plumbers/gas engineers, just get a few quotes, and also check the boiler specification for max flow rate.
Couple of tips if you do get a new boiler be sure to specify exactly where the pipes go (if you change location), get one of the remote controls (very handy, and allows you to put boiler in loft), and also specify exactly how you want the magnaclean device fitted (collects sludge from central heating). Ours is unfortunately very prominent - we need to move it.
Also, we went for a really big powerful boiler, so more than enough water but tbh probably a bit too big for our house: bigger may not necessarily always be better.
I'd only get vaillant, glowworm, or worcester-bosch, btw.
Yes this is common in the UK.
The boiler will feed hot water into the heating coils in the tank as well as providing the hot water for the radiators.
The electric (or immersion) heater will be there either as back up (in case the boiler fails) or to heat the water on cheaper electricity (Economy 7) overnight.
There'll be a thermostat on the tank which feeds back to the boiler to turn off the heating when the water is hot enough, but other than that there's no direct communication between the immersion heater and the boiler. There might be communication via the timer used to control when each is turned on, but that's not usual.
Best Answer
1) The red line that is teed into the blue line after the check valve could be used as a recirculating line to provide almost instant hot water to all the hot faucets. Make sure that you add a check valve in that line so you do not get reverse water flow when a faucet is turned on. 2) The supply line to the heat pump should come from the bottom of the storage tank so it utilizes the coldest water to be heated, and not come off the hot supply from the storage tank. 3)The hot discharge from the heat pump should go to a separate tap near the middle of the tank if one is available. If a separate tapping connection point is not available I would then tee it into the cold blue line at the tank supply but after the check valve. 4) I believe that a circulation pump is required in the heat pump line sized as per the heat pump's instruction sheet. 5) One last thing, if the red line I mentioned in item #1 is for a recirculating line to insure almost instant hot water at each faucet it can stay as is and you will need to install a pump on that line to circulate the water (buy the smallest pump you can) Mine is a B&G NBF-8S 103257LF 39 watts. 6) you said that you did not show the cold supply (mistake).