Thermostatic showers

[Ben]

Hi all,

How quickly do thermostatic valves adjust to a sudden loss in pressure in one pipe? ;) Let me explain- In my flat I have a combi boiler for the hot water, mains pressure CW for the kitchen *but* a CW storage tank for the bathroom (apparantly first thing in the morning the pressure was very poor). Unfortunately the ceilings are very low so the head between the top of the CW in the tank and the shower head is at best around 50cm. Not exactly great then. I'm in the process of fitting a single vane booster pump to the bath / shower CW supply. However, my worry is this: if the water pressure really is rubbish I run the risk of using up all the water in the cold water tank and getting scalded. If I upgraded (from a standard mixer)would this help- would a thermostatic shower unit (like the Pegler Fanfare sold in Screwfix) adjust in time or would I be better with a hot water isolation valve (electrically switched) run off an electronic float switch in the cold water tank. Thanks for any advice,

Ben

[IMM]

Not that quick. You need a pressure equalisation valve on the hot and cold pipes to the shower.

Let me explain-

Sounds normal.

Use the shower via the combi whoch will be from the mains. The combi, and mains pressure, should be good enough for one shower.

Ben,

I;I'm not sure how your system is configured. Do you have a hot water cylinder? What does the cold tank supply? Is the combi off the mains? Is the mains pressure that poor you can't have a decent shower off the combi?

[Ben]

There's no hot water cylinder and the combi boiler is a non storage type. The cold tank just supplies the bathroom fittings (toilet, sink and bath / shower). The combi meanwhile is off the mains and seems to always give a nice powerful flow. So really it's the opposite of normal- high pressure hot water and low pressure cold (at least as far as the shower is concerned). Thanks for the info,

Ben

[IMM]

The hot and cold to the shower should be both off the cold mains. they must be approx the same pressure. Any slight fluctuation sin either pipe, the equalisation valve will take care of. Remove the shower pipe off the tank.

[Ben]

Aha! That's where the problem lies.... The water supply to the house is pretty pathetic, consequently in the mornings there is limited flow. I think the person who installed the plumbing thought putting all the incoming water to the combi with a tank for the CW was a better idea. Then again, the ball c*ck will come making the pressure still drop... Confusing!!! Sometimes I think it would be easiest to take the water to the bathroom straight off the mains and scrap the tank!!! Any obivous disadvantages???? What kind of pressure differential will a pressure equalising valve manage? The plumbworld one says it prevents scalds- I'm assuming a

100% differential therefore. Anyway, I'm hoping a 1.5bar shower pump will roughly equal the pressure coming out of the combi boiler and all will be good! We'll see! Is it still a requirement to fit flap valves or will the PEV effectively do this automatically. Thanks for the info- I'm more a sparky person myself, plumbing is a new field for me.... Very confusing!

Ben

[Pete C]

Hi,

Have you measured the CW flow in the morning to see what it is? It may be that the boiler needs a minimum pressure and the separate tanked CW supply helps maintain this.

Try running the shower hot in the morning while all the cold taps in the kitchen are open. If the combi doesn't cut out and the flow is satisfactory just take the shower cold off the mains.

cheers, Pete.