Unvented central heating losing pressure only in winter

[JohnD]

Thank you all.
I have wrapped sandwich and no water.
The pressure doesn’t go more than 1 .5 bar which I topped up.
It is only winter time when central heat running, day one it is at 1.5bar and day two

Do you mean you did not run a test with CH on?

 

[Selvara]

Just to update on this low pressure issue with unvented system during winter.
I noticed today afternoon when system is cold it no hot or hear running the pressure gauge at unvented hot water cylinder showed zero but when I started central heating with out topping up water the pressure increase automatically to 1 bar with out topping up.
I wonder why pressure goes to zero when system is cold and when I start heating it goes to 1 bar with out topping up.

 

[Harry Bloomfield]

I wonder why pressure goes to zero when system is cold and when I start heating it goes to 1 bar with out topping up.

As the temperature of many things is increased, the expand to occupy a greater volume. Water also does this, hence increasing the pressure in a sealed system.

 

[danfre]

Looks like the cylinder temperature and pressure relief valve is connected to the heating system

 

[JohnD]

...when I started central heating with out topping up water the pressure increase automatically to 1 bar with out topping up.
I wonder why pressure goes to zero when system is cold and when I start heating it goes to 1 bar with out topping up.

1) thermal expansion

And

2) expansion pressure vessel not working. Might need to be pumped up or replaced.

 

[JohnD]

The reason for my earlier post.

Not "leaking"

If the pressure goes up too much when the water in all the radiators is heated and expands, the Pressure Relief Valve purposely releases some of the hot water to relieve the excess pressure.

Likely it is not the PRV that is the cause of the problem.

Next time you top up the water, photograph the pressure gauge on your boiler when it is cold. Then turn on the heating and photograph it again after 10 minutes, 20 minutes, 30 minutes, and when fully hot. Then photograph it again when it is fully cold. Wild swings in pressure indicate a problem with your pressure vessel.

 

[Selvara]

Thank you very much.
I will get gas engineer to look at expansion vessel.

Just to add a few details that I have noticed after two days pressure goes down during winter then one of the radiator upstairs has no water when bleed.
Could it be some gas in the system which causes pressure to down ?

 

[Madrab]

Could it be some gas in the system which causes pressure to down ?

Possibly but the water in the system would need to be going somewhere if a rad is emptying, Only three places it can go, out the PRV, out a connection/rad/pipework on the system as a leak or through the Heat Exchanger (HEX) and out through the condensate pipe if it's a condensing boiler.

Is the system water black?

 

[JohnD]

Thank you very much.
I will get gas engineer to look at expansion vessel.

Just to add a few details that I have noticed after two days pressure goes down during winter then one of the radiator upstairs has no water when bleed.
Could it be some gas in the system which causes pressure to down ?

Air in the system would help it absorb thermal expansion, so I think not.

 

[Selvara]

I want to update back to the forum
1. when system is not running, the pressure gauge shows ZERO bar (whole day central heating was on at 19'c), when i started the central heating to 21'c today the pressure is automatically increased to 1 bar with in 5 mins. does this indicate a leak? if water is escaped somewhere i wonder how pressure is increasing one bar.
2. i also noticed out side of the pipe connected to boiler (Worcester Telescopic 350 mm - 570 mm Horizontal Flue Kit) is dripping dot dot when heating is on and stopped dripping when heating is off. what does his indicate?

 

[JohnD]

does this indicate a leak?

No,

1 ) Your pressure expansion vessel probably needs pumping up or replacing.

2 ) Your pressure expansion vessel probably needs pumping up or replacing.

 

[Selvara]

thank you. appreciate it.

 

[Harry Bloomfield]

No,

1 ) Your pressure expansion vessel probably needs pumping up or replacing.

2 ) Your pressure expansion vessel probably needs pumping up or replacing.

I disagree, I think the expansion vessel probably needs pumping up, or replacing.

 

[Selvara]

Is these two not same ?Expansion vessel and pressure expansion vessels

 

[JohnD]

Yes.