pressure drop off from hot water taps

[Jonny7]

Is it normal, on a combi boiler set up, for the hot water flow from any tap to drop off as you increase the flow from the adjacent cold water tap? Or is that the symptom of bad installation or even a problem somewhere. The system as a whole is probably no more than 2 years old at the most. The make of boiler is not one I'm familiar with but cannot recall the name here at work (It has enough flashing LEDs at the bottom to take a part time job in a disco).

The reason I ask is that the new place I've bought has an electric shower which is feeble and I want power! So I bought a mixer unit (for use with combi boilers it says on the box) but can foresee a load of fiddling with the temp and flow controls just to get a decent shower.

The alternative, apart from a new boiler and hot water tank system, is to install a separate hot water tank just for the shower. I'd have to heat this with an immersion heater but it would be worth it to get that elusive decent shower. If I went for a hot water tank (which I'd have to buy anyway if I switched boilers) I'd need to have a vent. What would be the best way to do that, non return valve and short copper stub into the loft space (where the tank would be anyway) or is there another way it's usually done?

Appreciate any responses,
Thanks,
Jon.[/i]

 

[Gasman1015]

Yes, its normal, how much it affects it depend on your mains pressure and flow rate plus the flow rate available through the boiler.

If you are going to put a hot water cylinder in then you can plumb it into the combi just like a traditional system, the vent off the cylinder should be 22mm , and terminate at the cold tank, do not put any valves in this pipe.

 

[Jonny7]

Thanks very much for that Gasman1015. I've actually been looking into the whole aspect of hot water systems and did wonder if you could feed the coil of an indirect cylinder via a combi boiler.

The trouble with that might be that in the summer, a combi boiler wouldn't have a hot water setting so you'd need to isolate all the radiators and turn the room stat above ambient? Or just use the immersion heater on a timer.

I was wondering (given that I do not have a cold water tank) if I might be better off installing an unvented sealed system? Would this then give equal pressure for both the cold and hot supplies to a mixer shower (and similar flow rates)? I could then have the option of installing a pump for even greater power and thus end my days helplessly pinned against the far bathroom wall by the sheer power of my shower

 

[Gasman1015]

You misunderstand me, replumb and rewire the combi as a traditional system, s or y plan.

Yes, you would need a cold tank if you want a gravity hot water cylinder.

Yes, unvented hot cylinder will give equal pressures but again will depend on your existing mains, you can throw lots of cash at it and boost the mains using an accumulator, such as OSO.

 

[Jonny7]

Ah right, I see what you mean about replumbing etc the combi to a traditional set up. I also see what you mean about throwing plenty of cash at it!

I think the unvented hot water tank requires certification from what I can see regarding it's installation. Coming from a petrochemical background, anything that involves pressure relief and over temperature sounds like a potentially tricky situation if you do not install it correctly.

So I think for a simple stand alone feed system for my shower, I need a hot water cylinder (immersion heated overnight on a timer) a cold water tank to feed the cold supply and also to vent the hot water cylinder into. That way, I'll have equal pressure (depending on them being next to each other) and equal flow. That lot should be under £200 I'd have thought on a DIY basis? Then if I need to boost the pressure, I can fit a twin pump.

I'd still need the hot water and cold tanks if I replumbed the combi anyway, the only other alternative would be to get a pressurized, non vented cylinder fitted by a plumber who could then certify it. I've no idea what that would cost but if it came in at around £250 - £300 inclusive .... but I somehow doubt that. I imagine the tank would be at least that?

Is that a fair summary do you think Gasman1015? Appreciate your responses so far BTW.

Jon.

 

[Gasman1015]

Personally, I would prefer the gravity setup, especially in your case because of the mains pressure problems you are having.

Yes, you need a ticket for unvented and the tank alone can cost between £400 - £ 600.

£200 will get you cylinder, tank and a shower pump.

Good luck.