Poor performance shower with new combi

[Donald Trefusis]

Hello Newsgroup,

Recently had a "combi" Vaillant boiler to replace our old boiler/tanks/shower pump. I was assured by the plumber that the water pressure for the shower (upstairs) would be as good as or better than the pump we had. Needless to say - it isn't! I have read about a system called Megaflo and I was wondering if this could be added to our combi boiler? There is no way we could afford to have the combi taken out and new conventional boiler put back in. Any ideas how to get a better flow/pressure?(I know I am being imprecise but I hope you understand what I mean!)

Thanks for your help.

Don.

[Christian McArdle]

If you can't afford to replace the boiler again, you can't afford the Megaflo. However, the Megaflo would be perfectly happy sitting on the combi. The combi water system could then supply a kitchen tap or something.

On the other hand, we'll need more information about your system to see if it is working properly. Take a large container of known capacity and time how long it takes to fill it from the hot taps at various locations to calculate the flow rate. In particular, test the kitchen hot tap and the shower head. Make sure you don't turn them on so much that the water goes cold. What flow rate are you getting?

Also, what boiler do you have? In particular, is there a number somewhere between about 24 and 35 written on it anywhere?

Christian.

[Donald Trefusis]

Can afford Megaflo, but not Megaflo AND new boiler!

I'm not sure I understand what you mean - the combi can be used to "feed" the Megaflo? I though I would need a non-ombi boiler for that.

OK - I'll try and do that tonight.

TurboMAX plus 828E

Thanks for you help,

Don.

[Christian McArdle]

The only difference between a combi boiler and a non-combi boiler is the addition of the instantaneous water heating function. The combi boiler can do anything a traditional boiler can do, including heating a hot water cylinder such as a Megaflo.

Christian.

[Christian McArdle]

You should note, however, that the controls may need rejigging. Any built in programmer will be pretty useless and require setting to 24/7. You will need an external 2 channel programmer and zone valves, just like a system boiler installation. These can control the boiler through the room thermostat wiring and may even need some sort of relay if the boiler requires volt free contacts and you are not using 2 port zone valves in a Honeywell 'S' configuration.

A basic set of controls will cost you under 100 quid, though. You would need a room thermostat (should already have one), a 2 channel programmer and 2 zone valves (2 port). You can often buy this whole lot as a matched kit for discounted prices. You may find it more complicated to go for a 3 port valve version, particularly if your combi wants a simple volt free contact switch as a thermostat. This is because the 3 port valve doesn't have "call for heat" microswitches, but must rely on the programmer outputs, which will be

230VAC, rather than simple switches.

Christian.

[Donald Trefusis]

Forgive my ignorance of these things - Thanks for all your help.

I wish my plumber was this helpful. He comes highly recommended from a number of my friends - but he doesn't seem keen to do anything other than install a standard combi. He persuaded me against installing a condensing boiler (said he hadn't installed any) which I'm starting to think was also a mistake....

[Christian McArdle]

Pretty standard for most heating engineers. However, looking around you can always find one or two that actually keep up with modern technology.

He'll have to look up his condensing boilers soon, though. Non-condensing ones are effectively being banned soon.

Combis are easier to install than storage systems. Condensing boilers are more difficult again. I wonder why he wants to install non-condensing combis...

Christian.

[Dave Plowman]

But are they when you already have the storage tanks etc? I can see that on a new build.

He obviously doesn't read the same trade mags as IMM.