some questions about how combis work...

[tan8856]

hi

our combi has a primary and secondary heat exchanger. why does it need 2? do they do different things?

if the heat exchangers have scale and magnite on them from the radiator system, doesnt potential drinking water that passes over them get contaminated? i assumed that with a combi you could in theory drink the hot water it creates as its not stored in a HWC and comes straight from the mains? there could at least be some left in the pipes when i go to pour a glass of cold water couldnt there?

how can a combi heat the rads and provide hot water at the same time? how does it separate the 2 flows?

thanks

 

[electronicsuk]

hi

our combi has a primary and secondary heat exchanger. why does it need 2? do they do different things?

The primary HX heats the sealed system water as used in the CH loop and is heated directly by the burning of natural gas in the boiler. The secondary HX transfers heat from the system water to the mains DHW output. DHW is not directly heated by flame.

if the heat exchangers have scale and magnite on them from the radiator system, doesnt potential drinking water that passes over them get contaminated?

No, a water-water heat exchanger does not mix the water in the two systems, merely transfer heat between the two by natural conduction of heat from an area of high temperature to an area of low temperature.

i assumed that with a combi you could in theory drink the hot water it creates as its not stored in a HWC and comes straight from the mains?

Correct.

there could at least be some left in the pipes when i go to pour a glass of cold water couldnt there?

How is that any worse than the water sitting in your cold water pipes all the time whenever a tap is not running?

how can a combi heat the rads and provide hot water at the same time? how does it separate the 2 flows?

It can't. You either get CH or HW, and this is controlled by a diverter valve.

 

[kevplumb]

View media item 1024
if you pick the number im sure somebody will tell you what it is / does

did have it typed but lost it and can't be assed to redo it

 

[tan8856]

very interesting thanks

sooo...

The primary HX heats the sealed system water as used in the CH loop and is heated directly by the burning of natural gas in the boiler. The secondary HX transfers heat from the system water to the mains DHW output. DHW is not directly heated by flame.

how is the DHW heated when the CH isnt on ie during summer?

 

[kevplumb]

the diverter valve (21) closes the heating port off and the water flows between the main (16) and secondary (9) heat exchangers

 

[glasgowgas]

and this is controlled by a diverter valve.

 

[electronicsuk]

and this is controlled by a diverter valve.

Thankyou

 

[bengasman]

You haven't asked the most important question.

 

[tan8856]

You haven't asked the most important question.

which is what?

 

[glasgowgas]

You haven't asked the most important question.

cmon now Ben


View media item 15381

 

[bengasman]

You haven't asked the most important question.

which is what?

How much is a service?