No vent pipe on vented CH system

[Ed Sirett]

I have just chcked the installation instructions for Suprimas and indeed it does show that arrangement as being acceptable.

[BillP]

Vented CH system with feed and expansion tank in the loft. Potterton Suprima 80 boiler. Fully pumped S plan. Went into the loft to check that there was no crud in the F/E tank prior to draining down. Noticed that there was no vent pipe. Only 22mm feed/expansion pipe from bottom of cistern, 19mm overflow and 15mm mains feed to float valve. Anyone know when and why it became acceptable to do away with a separate vent pipe.

Thanks Bill

[BillP]

feed/expansion

Hi Ed,

I did the same thing and looked at the manual on the Potterton web site, and as you say it does show a combined feed/vent.

I'd never seen it before and was surprised to see it as being acceptable. It just didn't seem right.

It just hope nobody ever adds a service valve in the airing cupboard in the fill line thinking it'll make life easier. If the system's ever run and the gate valve is shut, no expansion no vent.

I know service valves should never be fitted in the feed/expansion line but I've seen a few fitted because people have thought it makes life easier. Sooner or later it will happen.

Bill

[IMM]

They are not new. Today they are acceptable in boilers with high limit stats. In other words a run stat and a high limit so less chance of boiling over if one fails. Many modern boilers, especially combi's, have flow switches in the primary circuit. If the pump is down or no water, the burner locks out. It is a good idea to fit one on a boiler that does not come with one as standard. It can save the boiler, especially with a sealed system with no auto fill up.

I know of a Ravenheat combi that burnt out because there was a water leak. The water emptied, pump burnt out and the burner kept going....expensive kaput.

[Ed Sirett]

Yes with NO vent, just direct into the tank outlet.

Perhaps becasue the boiler has over-heat lockout protection.

Hopefully sealed systems are becoming the norm, also there is a chance that someone will spot it before it does trouble.