Confused about heating??

[Bagpuss12]

I have a Main Combi 24 boiler which is regularly serviced and as far as I am aware if working ok. My system has no leaks that I am aware of but I have encountered a situation that is baffling me??
The boiler is on timed and comes on twice a day wherbey the pressure is up where it should be between 1.5 - 2 bar. However, when the boiler clicks off and cools down the needle drops to zero?? Then when it clicks back on it works and goes up to the required pressure. Its almost like it is losing pressure but then re-pressurises itself when it comes back on?? Is this possible??

 

[Dan Robinson]

Guffed expansion vessel.

 

[Bagpuss12]

Is that something that would show up on a service as I'm due one soon or do I need to call the engineer?

 

[CBF]

some do some don't, i personally don't check unless the customer tells me there is a problem as the boiler needs draining to check the EV pressure

 

[Bagpuss12]

So as long as I flag it up with the service engineer he should investigate??

 

[CBF]

yes he should

 

[Bagpuss12]

Would the problem with the expansion vessel affect my hot water flow at all? It's nowhere near a quick as the cold water flow?

 

[Hugh Jaleak]

Hot water flow is a seperate problem, not related to the expansion vessel. May be result of a limescale build up, depending on your water type.

 

[McCombi]

Would the problem with the expansion vessel affect my hot water flow at all? It's nowhere near a quick as the cold water flow?

If the hot flow was same as cold, water wouldn't get hot enough as it would pass through boiler too quickly to heat up.combi boilers usually only give you approx 35'c temp increase (from cold temp at tap to hot temp at tap). At a specific flow rate, usually around 11 litres a minute, but all boilers different.