Boiler losing pressure only on central heating

[SnosRap75]

Hi, I have a Worcester 28i junior boiler that has started to lose pressure, only when using the central heating. When using hot water I have no issue, however, when running the heating the pressure drops. Im looking for some ideas on what could be causing this. I have no sign of pipe leaks, although they could be hidden. Is it possible it could be the boiler, even though I see no water leaks?

 

[ShaunCorbs]

Expansion issue so needs a gas safe engy to fix as the prv will need to be changed

 

[SnosRap75]

Expansion issue so needs a gas safe engy to fix as the prv will need to be changed

Hi. I was hoping it would be something along those lines rather than a leak. With it only being when I used the heating I was convinced it was a pipe leak and currently see not water anywhere. Was worried it was hidden somewhere. Would I expect to see water coming from the over flow in this case or not? Thank you...

 

[ShaunCorbs]

Hi. I was hoping it would be something along those lines rather than a leak. With it only being when I used the heating I was convinced it was a pipe leak and currently see not water anywhere. Was worried it was hidden somewhere. Would I expect to see water coming from the over flow in this case or not? Thank you...

Maybe but only when the system is fully hot

 

[SnosRap75]

Expansion issue so needs a gas safe engy to fix as the prv will need to be changed

Also, the pressure increases to 3 during the heating cycle. It did then come down again.

 

[ShaunCorbs]

Also, the pressure increases to 3 during the heating cycle. It did then come down again.

Which probably would the prv letting some out or it cooling down

 

[SnosRap75]

Which probably would the prv letting some out or it cooling down

Ok great...really hoping it wasn't a leak.