Low water pressure system boiler

[pdug05]

Hello, we've Recently moved into a new house which has a modern looking unvented Worcester boiler with a megalo tank. Water pressure in the property is pretty disappointing and flow from both hot and cold taps is no where near our previous house.

Doing a bit of spring cleaning and bled all the radiators and noticed I had to repressurise the boiler which is located in the loft.

Water pressure downstairs is approx 1.5bar with a flow rate of around 12l/min from the kitchen tap. Now when I had to repressurise the boiler (Worcester) I couldn't pressurise beyond 0.7bar and the low pressure error kept appearing on the boiler interface. I couldn't understand at first why I cant get beyond 0.7bar but given the system is in the loft I believe that must be the cold water pressure at this elevated point.

I have managed to pressurise and restart the system to fire up, now during operation the central heating pressure does get to 1.3 and the house is nice and warm. Warm water flow rate from the megaflow is just about manageable but poor, I believe this is determined by the low cold water replenishment pressure in the loft?

My question is are there any simple quick fixes to improving water pressure in the loft of our house? Our house is a 1960s build and I assume the water is brought in via an old 15mm pipe, replacing this would be difficult. Can the water be pumped from the ground floor to loft improving pressure up there? Thanks

 

[Deleted member 267285]

Sounds like you might need a G3 registered engineer for your invented cylinder. The pressure for the boiler night be a faulty filling loop valve too.

 

[oldbuffer]

1. Assuming you have a two storey (ground plus first floor) house the pressure drop between floor of ground floor and hot water cylinder will be roughly ((height of two floors (in metres) / 10) bar). With 1.5 bar in you should have roughly 1.0 bar at the floor of the loft.
2. Pressure:
2.1 A pressure of 1.0 bar is not really sufficient for an unvented cylinder, you really need a minimum of around 1.5 bar of dynamic pressure.
2.2 Dynamic pressure is the pressure measured at an outlet with at least one other mains fed outlet running.
3. Flow rate:
3.1 For an unvented cylinder you need nearer 20 lpm for satisfactory performance.
3.2 If measured at the kitchen tap, there may well be narrow bore isolation valves and restricted flexible hoses which reduce the available flow rate at the tap spout. If you have an outlet without restriction (such as a garden tap, although that should have an isolation valve) re-measure the flow rate.
4. I'd be interested to know how you got the boiler up to 1.3 bar from a 0.7 bar source.

 

[pdug05]

Thanks for the replies

I've checked the flow rate at the garden tap and it's 12l/m max. So like you say, no where near enough for satisfactory performance of the system.

During operation of the boiler doesn't the pressure in the system increase? Hence why it goes from 0.7 to 1.3bar?

 

[oldbuffer]

1. The pressure only increases within the boiler's primary circuit, which heats radiators and the coil in the hot water cylinder. It has no effect on the pressure of Domestic Hot Water (DHW).
2. With an unvented cylinder, the DHW pressure can never be higher than the incoming mains pressure. Hence the need for pressure (and flow) measurements before installation.
3. The primary circuit pressure can increase during operation because it is sealed. As water is heated it expands, and as the system is sealed, this expansion leads to an increase in pressure. This increase is accommodated in an expansion vessel. When the water cools, the pressure reduces. The system pressure should be measured with the system cold.