blowdown running constantly?

Your flat plate heat exchanger is leaking allowing the cold mains water at a higher pressure to leak into the boiler and CH system .That is why it is significantly higher when your run the hot tap as the cold water then circulates thro' the flat plate the boiler's own hot water is directed on a priority basis also thro' the exchanger but in its own seperate tube if there is a leak in the tube mains pressure enters the boiler water and hence the high pressure lifting the safety valve.

Guytawe
June 2010

the blowoff valve may need cleaning or replacing or you're putting too much pressure in the system it should be about 1.5 bar another possibility is you have problems with the pressure vessel this will show up by the pressure gauge rising and falling very rapidly with the introduction or loss of a very small amount of water

brian
June 2010