Gas boiler with backboiler possible with open vented system?

[rockofages]

Our gas boiler is about 18 years old and is due for replacement. We want to get a modern condensing boiler with assistance from SEI.

I spoke to one plumber about it and he said modern natural gas boilers will not operate on an open system, and that if we want to keep the open fire we need to go for oil instead.

He says if we want a modern gas boiler we have no option but to get rid of the backboiler and go for a closed system.

A quick google shows that condensing natural gas boilers are available for open system.

Why is the plumber telling us this?

 

[DavyJones]

Don't know, get another plumbers opinion.

The Baxi solo is a HE boiler that is open vented.

 

[DGOBS]

I agree Davy, but manufacturers of gas boilers do not allow them to be installed on shared water systems (no mixing of back boiler water with gas boiler water) and are actively voiding warranties for this practice.

 

[Brianne]

We have gas fired central heating and a back boiler from an open fire in the sitting room. We had to get a special boiler and it was a bit more expensive, we can run the two systems together with no problem but we got the systems in at the time of the build.

 

[rockofages]

Brianne - what model is your gas boiler? Thanks.

 

[Brianne]

Sorry for delay in replying. Our boiler is a ferroli sigma boiler, I know nothing about it but we had to order it and wait for it as it is designed to work with the open fire back boiler system and it was more expensive than usual. Cost about 1500 Euros in 2006. Both systems have worked together with no problems since installation.

 

[DGOBS]

In no way is the Sigma a special or unique boiler, it was chosen to be used in this fashion as it has a cast iron heat exchanger (as do a fair few others, ideal classic, Baxi solo etc)
and still should not be used on a mixed water system, the only reason they are chosen by an installer is the fact that the cast iron heat exchanger acts as a heat sink meaning the boiler is less likely to trip on its hi limit stat when subjected to excessive heat from a back boiler. This boiler would not be classed as a hi eff boiler (most likely class d)
and should have not cost any extra!