Worcester greenstar 25i Erp combi boiler. Re-pressure

nick1234

Hi

i just had a question on increasing my boiler pressure which seems to fall when the hot taps are on but then returns to green.  The boiler has been serviced but below the boiler there is a nob you turn and a key which i dont know if i leave open or closed and when re pressurising do i close then open?  I see conflicting information online

Pictures below 
thanks

nick1234

Its currently in the open position..

bjorn_toby_wilde

https://www.worcester-bosch.co.uk/heating-advice/boiler-pressure

The fact that the pressure drops when the taps are turned on suggests the filler loop hasn’t been closed after repressurising.

WIAWSNB

What are the actual respective pressures, off and running DHW? By how much does it change?

Ayr_Rage

With the system cold.

Push the white key up and twist to lock (read the manual).

Turn the square knob to let water in and pressurise the system to 1.25, close the knob.

Bleed your radiators 

Reset the pressure to 1.25, close the square knob, twist and remove the white key completely and put it somewhere safe.

Dry the area and make sure there are no leaks.

See what happens when you draw hot water.

(The pressure WILL increase marginally when the CH is running)

WIAWSNB

Ayr_Rage said:

With the system cold.
Push the white key up and twist to lock (read the manual).
Turn the square knob to let water in and pressurise the system to 1.25, close the knob.
Bleed your radiators 
Reset the pressure to 1.25, close the square knob, twist and remove the white key completely and put it somewhere safe.
Dry the area and make sure there are no leaks.
See what happens when you draw hot water.
(The pressure WILL increase marginally when the CH is running)

Very helpful.

The mystery, tho' is that he says the pressure drops a bit when the DHW is being run, and then goes back up when stopped. That's a head-scratcher. 

Ayr_Rage

WIAWSNB said:

Ayr_Rage said:

With the system cold.
Push the white key up and twist to lock (read the manual).
Turn the square knob to let water in and pressurise the system to 1.25, close the knob.
Bleed your radiators 
Reset the pressure to 1.25, close the square knob, twist and remove the white key completely and put it somewhere safe.
Dry the area and make sure there are no leaks.
See what happens when you draw hot water.
(The pressure WILL increase marginally when the CH is running)

Very helpful.

The mystery, tho' is that he says the pressure drops a bit when the DHW is being run, and then goes back up when stopped. That's a head-scratcher. 

Yes, that's the issue, but getting the heating side up to pressure , the key out and knob closed isolates that from the mains water inlet.

I've a feeling this could be a long topic.

FreeBear

WIAWSNB said: The mystery, tho' is that he says the pressure drops a bit when the DHW is being run, and then goes back up when stopped. That's a head-scratcher. 

If the filling loop is open and there is no non-return valve (or it is faulty), that would explain a drop in pressure.

Normally, the pressure should increase when every the boiler is running regardless of whether it is "doing" heating or hot water.

WIAWSNB

FreeBear said:

WIAWSNB said: The mystery, tho' is that he says the pressure drops a bit when the DHW is being run, and then goes back up when stopped. That's a head-scratcher. 

If the filling loop is open and there is no non-return valve (or it is faulty), that would explain a drop in pressure.

Normally, the pressure should increase when every the boiler is running regardless of whether it is "doing" heating or hot water.

Surely only if the mains water pressure was utterly pitiful? 

bjorn_toby_wilde

It is in many areas. You’d be surprised.

Many water companies only guarantee 1 bar

FreeBear

bjorn_toby_wilde said:

It is in many areas. You’d be surprised.

Many water companies only guarantee 1 bar

Just topped up my boiler after having a service. In the past, pressure was around 1.4 bar. Today, a measly 1.2.