IMHO if a flushing toilet has a significant effect on your hot water then it is a problem with the installation or water supply not the type of boiler you have. Current I have a combi boiler and flushing the toilet has negliable effect on a shower. I can't say the same for the previous storage system.
On Wed, 16 Jan 2008 09:46:34 +0000 someone who may be Mark wrote this:-
Certainly a problem with the installation in the storage system. A separate pipe should have been taken from the cold water storage tank, directly to the shower and feeding no other fittings. Then flushing a toilet would have no effect on the shower.
If you have mains water pressure at the bottom end of the scale - and very many do - then other use of that main while showering might well effect things with a basic shower unit.
Good design of a storage system can prevent it showing this effect. It's not really possible to modify a poor mains water supply.
The same with a combi: a separate dedicated cold feed pipe back to mains stoptap. And all water appliances balanced so as to not rob the combi or shower.
Even here with good pressure, a refilling cistern has a *noticeable* effect on hot water pressure/flow.
I suspect the culprit is the softener. Its not enoughto worry about and hot and cold rates are affected equally so its not irriting in terms of temp changes.
The shower must have its own dedicated cold feed from the cold water tank, then no influence from the cold services. Also the cold feed from tank to cylinder must be large enough to cope with shower and another draw off - this must be dedicated to cylinder supply only. That is why it is usually
28mm. The shower hot supply directly off the cylinder too.
Cold water tank/cylinder setup is a little complex and pipe intensive and expensive to install.
Take a diagram of a cold water tank/cylinder system and turn it on its side. Replace the tank with the cold water mains, the DHW cylinder with a combi or unvented cylinder or heat bank and that is how a mains pressure system should be fitted, using smaller bore pipe where necessary.
If shower fed from mains, then flushing toilet fed from header tank would cause level in the tank to drop, ballvalve to open, leading to a drop in the mains pressure as the mains has now to feed the header tank as well to replenish the water used.
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