Megaflow - Undersized (15mm) water main

We live in a 1960 - 1970 build house and planning to do the loft conversation.

We like to install a Megaflo or comb boiler so that we can get a good water pressure in our Loft. There will be total two bathrooms in the house and one W/C

The main water pipe coming in the house is undersized probably 15mm and we can't change the main pipe from the water meter as it supplies water to our neighbor as well.

I think the per minute water flow in the first floor toilet is 11L which is way below 20l/m recommendation.

What are our options? Can we replace the 15mm pipe half way through the main to our house then bring it all the way to loft? Or can we just replace the 15mm pipes in side the house?

Thank You

If 11l/min is the most you can get from your main then you may as well have a combi boiler

You can still change the pipe if it supplies the neighbour! Why wouldn't you? Neighbour would also be happy with better supply.

bsr said:

You can still change the pipe if it supplies the neighbour! Why wouldn't you? Neighbour would also be happy with better supply.

Click to expand...

Thames water would need to change it and it's not cheap.

I tested the water pressure in our garden tap today and its 15l/m and on the first floor bath its around 10l/m.

Is there any option of using a pump without installing a mega flow or combi boiler?

1. You are measuring flow rates, NOT pressure in your post #5.
2. Pressure is measured in bar and requires a special gauge to measure.
3. Pressure for an unvented hot water cylinder needs to be around 2.0 bar. This is to be measured at one mains connected outlet (e.g. outside tap, washing machine tap) with another mains connected outlet (e.g. kitchen tap) running. Called the dynamic pressure.
4. Water is essentially incompressible, so broadly speaking the best flow you will get for a given pressure is determined by the smallest pipe it has to flow through. Adding a wider pipe after a smaller one will make no difference.
5. You can install a pump to provide additional pressure to all but the kitchen cold tap. You need a "universal" type pump, not a shower only pump. Such a pump takes it water from the cold water storage cistern (CWSC) and the hot water cylinder (HWC). There are rules for the size of CWSC and HWC, for the connections to them and for the placement of the pump. The rules are fussy but not difficult, but must be followed for a successful installation and a valid warranty. The biggest drawbacks are the need for separate feeds to the pump from CWSC and HWC. Unless there is an electricity supply nearby additional electrical work might be needed.
6. Have a look at Stuart Turner "Monsoon" pumps. Expensive but good, quite critical if you are pumping almost everything.
7. The pumps do make a noise while operating. Can be an issue at night if a WC is flushed for instance.

The dynamic pressure is around 1.4-1.5 bar.

The static is around 2.7 bar