CH pressure variation

[fred]

What kind of variation should I expect between off and running? Off (cold) it's about 1.5 bar rising to around 2 bar when hot. New system, Worcester Bosch Greenstar 30cdi Cheers.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "fred" saying something like:

That's perfectly normal.

[<me9]

Sounds nearly right. Shouldn't cause a problem. Unless multi storey I would expect 1 bar rising to 1.5 but what you have is ok. If the hot rises much above 3 the relief valve may open and ditch some water. 1.5-2 is slightly high but acceptable.

[EricP]

That's fine, although I would check the instruction book as 1.5 is a tad high for cold, but nothing to worry about.

[gazz]

i have my (halstead combi) at 1 bar cold, it goes upto 2 bar when hot, prolly a result of the mix of 15mm an 8mm microbore pipes in the system, (2 rads are on microbore, the rest on 15mm, why i dont know, but the ones on the microbore heat up faster than the 15mm ones)

The central heating in my motorhome sees an even larger cold to hot pressure differance, but that runs at 85 degrees C rather than the 55 a home system runs at,

[Andrew Gabriel]

It depends on the vertical distance between the guage and the highest point on the system. If you have 30' or more above the guage, you will need more than 1 bar.