Shower Pump attached to combi question

[CLairehead]

Hi Everyone,

I am currently training my local college and we get lots of companies coming in doing presentations about their products. This week we had a rep from a well known shower company come in.

He said that it was against the law to "pump mains water" hence the reason why aqualisa sell a gravity and non gravity version of the digital showers. He also went on to say that if you are on a combi, you run the risk of sucking the water out of the boiler faster than it can heat it, resulting in a damaged heat exchanger.

I asked two questions, neither of which he could answer so I'm asking on here in the hope of a better response. First question was, if it was illegal to pump mains - how can a pressure washer be legal?

Second question was, why can't I stick a shower pump on to a combi setup and put a restrictor on the discharge of the pump(s) to reduce flow and not suck the water out from the boiler?

Hope someone can answer my query

Thanks

Claire

 

[Corgigrouch]

Answer to your first question is that you aren't actually pumping the water out of the mains, A pressure washer is pressurising the water that is supplied to it from your tap....The pressure washer supplies a low volume of water at a high pressure..... Having said that, my next door neighbour is still on a lead service pipe and rather than doing what I have done and dug a trench and fitted a new supply, he has fitted a pump which works well.... We used to be on a shared supply so if we were still sharing the supply I would have been pretty peeved if we both tried to use the water at the same time.... And I guess that he'd have had fizzy water...

I can't see sucking water through a combi with a pump being too much of an issue as the water that is pumped out will be replaced..... However, if you exceed the boilers flow capacity, then your water would be not as hot and your shower might not perform.... Fitting a restrictor to the shower would throttle the shower and the performance of the shower would reduce, possibly to the same performance that you would have with the combi on its own with a non pumped shower... So you would have spent more cash for no more performance....

 

[CLairehead]

thanks for that reply corgigrouch. Although this has left me even more confused!

Doesn't a pump simply increase the pressure of the water, hence a pressure washer is technically pumping and also isn't your neighbour "pumping" mains as well suggesting the aqualisa man was talking rubbish?!

Thanks

Claire

 

[CharteredEngineer]

In large buildings, a pump is often used to send water to the top of the building, however there is often an air break and a separate tank so its not technically pumping mains.

Personally I cannot see an issue with bolting a shower pump onto the mains provided you can get sufficient flow. If you are on an inlet restriction then the pump is likely to cavitate. Much better to gag in the discharge

 

[ChrisR]

Pumping the mains without permission from the water provider is illegal, though it can be permitted within strict performance limits. You have to apply for permission - it's most unlikely that your situation will be bad enough to qualify, because the amount and pressure you are deemed to need, are crummy.

The overriding concern is that by "sucking" from the mains you can affect other people's supplies.

First question was, if it was illegal to pump mains - how can a pressure washer be legal?

Their volume output is quite restricted - special rules apply to those.

Second question was, why can't I stick a shower pump on to a combi setup and put a restrictor on the discharge of the pump(s) to reduce flow and not suck the water out from the boiler?

WHat are you trying to achieve?
You can only have the flow through the combi that will get heated by its kWatts, typically about 10 litres/minute.
If you have less flow than that, you must have awfully low pressure mains, or very restricted pipework. Normal pipes will do it with about 1 bar mains pressure, without bother.
The other normal way you can vary things is to increase the pressure, but use a shower head with smaller holes, so you get fine, higher speed jets for the same litres per minute as before. For that you'd have to have a "break tank" (= a big cistern)somewhere, and pump water from that INTO your combi. That's only normal in eg 4th floor London flats with poor mains supplies. Plumbers know better than to try pumps on the outlet of a combi - it's illegal and you'd probably bust the pump.
Often better, find a shower head which is designed to "save water!" which they do by introducing air into the water flow so it feels better, at lower water flow rates. Common, and getting cheaper these days.

From another CEng - who's also a qualified plumber and knows something about water regs, combis and showers!