Condensating Boiler - Return Temperature

[Adyonline]

I'm Confused (easily done!)

I'm installing a Grant 15/26 vortex oil condensing boiler and within the documention it states that the return temperature must not fall below 40 degC and Ideally will be at 50 degC with a differential temperature of 20 degC, the reason being that the resulting condensate will corrode the heat exchanger. I spoke to the technical dept in Grant and they confirmed this.

Yet when I research Condensing Boilers on the Internet it seems that the whole point of a Condensing boiler is to have a low return temperature to allow it to condensate and without which its efficency will drop. Condensing boilers are supposed to be ideal for systems with a low return temperature (as low as 35 degC). This appears to contradict Grants requirements !!.

I'm fitting the boiler in a 5/6 bedroom and I'm conserned that the return temperture will be too low and I wont be able to maintain an economical and non-corroding system without some sort of indisciminate loop back from the feed.

Can anyone explain this or have any ideas of what can be done to maintain a 20degC differential.

Cheers,

Ady.

 

[Slugbabydotcom]

some sort of indisciminate loop back from the feed.

AKA a bypass! Fit a gate valve on the bypass and adjust it until you achieve the desired temp difference. Then take the wheel off the valve so that no-one messes about with it. Or you can buy a purpose made by-pass valve which is what I call 'exactly the same but different'

 

[Adyonline]

Yup - But I dont really want to fit a bypass as it will increase the cycling of the boiler - therefore reducing efficency. Is there another way such as a thermostatic type system ?