I've just installed a full hot water system which is working well and my existing pump is supplying reasonable pressure.  However, I noticed that if both showers are in use at the same time there is a slight drop in pressure.  The existing pump is a 'Pressure Drop' type, i.e. it comes on automatically when water is demanded at any outlet - pretty standard in Thai houses.  The pump is a fairly cheap variety, about 5 years old and has stuck before now so I decided to replace it with one a little more powerful in the hope that it might cope better with the additional demand of the hot water system.

 

However, I only looked at the wattage and flow rate when choosing the new pump - it was not until I got it home that I noticed it is of the 'Constant Pressure' variety.  I'm fairly handy and can tackle most jobs but I'm not a plumber and know nothing about pumps.  My question is, is it OK to replace my pressure drop pump with this constant pressure one?  I can't see a problem but I'd rather be safe than sorry.  I am unsure if any non return valves have been used in the house's plumbing as most of it is enclosed in concrete. I can get to the mains supply pipe as it enters the property and before it gets to the storage tank so it wouldn't be a problem to fit a nrv there if needed.

 

I intend fitting the new pump during my next trip in June but its still in its box so if I have made a mistake, I can easily go and swap it for a pressure drop type.

 

I also intend fitting a water filter in to the system at the same time to reduce the amount of calcium and protect my water heater, stainless sink etc.  I was told that I need a resin filter element to deal with calcium - is this correct?

A constant pressure pump is recommended for instant electric showers.

 

it works virtually the same way as your current one.

I am guessing you have installed some kind of multi point hot water system to mixer showers and now find the pump does not have enough capacity.

 

Swapping conventional with constant pressure pump will be fine providing its additional capacity can handle two showers to your satisfaction.

 

Example. A local Japanese guy had similar problem with his multi point hot water fed showers. He wanted five star hotel power when both of his showers were in use. The only way my uncle could satisfy this request was to supply a multi stage constant pressure pump that could handle the demand without noticeable drop in pressure. 

6 hours ago, Fruit Trader said:

I am guessing you have installed some kind of multi point hot water system to mixer showers and now find the pump does not have enough capacity.

More or less yes.  What I've installed is an Air Source Heat Pump.  Its fed by a simple connection to my cold water supply. The device has an internal pump which provides a small boost in pressure but it is only a small boost. The unit is self contained and requires only a water supply in and out - nothing else is required and so far it works very well.  I have then taken a feed from the heat pump to the sink and shower in each of my 2 bathrooms and one to the kitchen sink.

 

The drop in pressure I'm experiencing is very small and only noticeable when both showers are on at the same time.  However, as I mentioned in my original post, my pump is getting old and sticks occasionally so I decided to replace it.  Buy buying a pump that has a slightly bigger output, I'm hoping the drop in pressure I get when both showers are on will be gone.

 

What brand of pump did the OP install? Something like this?  http://www.heatthailand.com/products/th/Heat_Pumps