Pressure below 1 bar in morning when water heating comes on

[Alan stewart]

Got baxi 800 5 months ago with new water tank and expansion vessal which is opposite water tank.
After heating off all night and water heating comes on pressure too low below one bar makes noise.
If put central heating on pressure goes over one and is OK. Pressure stays under 2. Have recently had boiler guy round as was leak on expansion vessal which has replaced. But still have the above issue.

 

[ShaunCorbs]

Have you topped the system up to 1.2 bar ?

 

[Alan stewart]

Have you topped the system up to 1.2 bar ?

Hi thank for your response, I did top pressure to approx 1.2 hoping that would help when system cold and hopefully pressure OK when hot water set to come on in morning. When comes on is just below 1 bar still happened this morning so put central heating on and was OK stopped short of 2 bar

 

[Alan stewart]

Hi thank for your response, I did top pressure to approx 1.2 hoping that would help when system cold and hopefully pressure OK when hot water set to come on in morning. When comes on is just below 1 bar still happened this morning so put central heating on and was OK stopped short of 2 bar

Wondering if it's valves as only thing not recently replaced as had pump water tank boiler and expansion vessal new

 

[cjg]

it will be a neg pump. ie, drops a little when on, water heats up, presure will rise, leave it as it is and wait to see what happens

 

[Alan stewart]

it will be a neg pump. ie, drops a little when on, water heats up, presure will rise, leave it as it is and wait to see what happens

OK thanks, only thing is if you leave it it makes a fairly loud noise and can leave it for a few minutes and still makes noise, pressure low until putting central heating on then pressure goes up.

 

[ShaunCorbs]

Trying running the pressure at 1.5 bar cold and set when the pump isn’t on