Combi Boiler pressure valve

[DermS]

Hi,
I had a hot water and central heating system installed in a house in Italy last year. The boiler is a Simat Combi with a 60litre internal hot water tank.
The mains pressure outside the house is as far as I can tell is 6 bar. I was told a pressure limiter was fitted because of the high water pressure.
The trouble is that in the Summer when I only use the hot water everything is OK, but when the heating part of the boiler is also turned on in the Winter as well as the hot water at the same time, the pressure relief valve on the underside of the 60 litre tank lets cold water out when it starts up and drips on and off all the time about 4 to 6 cupfulls a day.
I am trying to get some idea of what might be causing this before calling out the so called boiler expert who does not seem very clued up at all!!
Any suggestions would be gratefully received.
Thanks

 

[chrishutt]

It sounds as if this discharge from the Pressure Relief Valve occurs when the hot water store heats up and expands. In the UK the expansion is accommodated by an expansion vessel, but in Italy it may be normal practice to let it discharge to waste.

However that doesn't explain why it only happens when the heating is on, so I wonder if the PRV is actually for the CH system water. If so, it indicates a fault with the CH expansion vessel. You need to give more information about system pressures. Are there not pressure gauges?

 

[DermS]

There is a gauge for the CHeating part showing a constant pressure of 1.5 bar which is normal for this boiler. No gauge for the hot water tank though!! But most of the water discharges as soon as the system is turned on and long before the hot water tank heats up!! It only drips when fully up to pressure and the water in the 60l tank is hot.
Could it be caused by the mains pressure of 6bar being too high and not being limited by the boiler or outside limiter?
Thanks

 

[ChrisR]

Could be the pressure reducing valve is "letting by" - ie not doing its job any more. Or it could be that someone has just fitted a gate valve in ignorance of what is required- that would limit only the flow, not the pressure. A 3 bar PRV should be ok.

 

[DermS]

Thanks for your help.
I will now get the plumber and boiler expert from Simat to the house together and try and explain this to them. Anyone any good at Italian plumbing technical terms!!
Ciao D

 

[chrishutt]

Chiunque qualsiasi merce ai termini tecnici dell'impianto idraulico italiano!!

No, not me. That's babelfish. Just in case you don't already know about it.