Unvented questions

G

Goldspoon

Still learning - especially about central heating systems - so apologies if any of the next couple of questions are daft ones ;)

On a friend's unvented there are two motorised valves (S system): one en route to HW and one to rads.

1. Can both be open at the same time (hw and ch at same time)?

There is a stat on the cylinder that when I was there was set at 90 degrees. The friend did not know what this was for and "used the boiler to set the hot water temperature" and this was at 76 degrees.

I suggested that the HW water temp at the boiler only dictated the heat of the water going through the coil. The hotter the boiler HW temp then the faster the cylinder of water heated up. It was the stat on the cylinder that determined the temp of water leaving the cylinder for showers taps etc.

2. Am I right in what I suggested in the last paragraph?

3. If the cylinder temp was set at 90 and the boiler HW set at 76 then surely the cylinder would never be satisfied and so would never send instruction to say so. Am I correct?

4. The boiler has settings for HW and seperate settings for CH. Let's say we set hot water at 60 and rads at 80 degrees. If there is only one flow and return leaving the boiler and that water (via valves) is distributed to both HW and CH... how does the boiler manage to supply two different temperatures of water. This is related to question 1 as the problem arises if both CH and HW are on at the same time I presume?


Thanks!
 
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Make of boiler and unvented unit would be useful. Be aware that the unvented will have two stats though. One operating stat normally set to around 60 and an overheat stat set to 90.
 
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1. Yes

2. The stat on the cylinder tells the motorized valve/boiler that the water is up to temperature. This closes the valve and tells the boiler to shut down unless a roomstat is calling for heat.

3.Yes. 90c is far far to warm set it to 60-65c. One stat is the overheat stat which is unadjustable.

4. The water at 80c that goes round the rads is the same water that goes round the coil in the cylinder. When the DHW is up to temp (60c) then the DHW valve then close. The water then continues to go round that rads until the room stat is satisfied.

Get it?
 
G

Goldspoon

SWB: Boiler is a Feroli or Ferolli and the unvented is a Telford Typhoon (sorry not sure of models).

Thanks Gplumb. I do understand... however what I do not understand is... if the water going through the rads is 80 and then diverts through the cylinder: cylinder stat says 77 for the HW and the boiler says 66 for the HW... which wins?
 
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SWB: Boiler is a Feroli or Ferolli and the unvented is a Telford Typhoon (sorry not sure of models).

Thanks Gplumb. I do understand... however what I do not understand is... if the water going through the rads is 80 and then diverts through the cylinder: cylinder stat says 77 for the HW and the boiler says 66 for the HW... which wins?


Its not a case of who wins, the water that is circulated at 80c through the system regardless of what the room stat or cylinder stat call for. The water in the cylinder takes heat from the coil and when that body of water( the water that comes out the hot tap) is up to temp (60c) the stat then tells the valve to close.

The boiler stat controls which temp the water leaves the boiler at, it may come back at 50c or 70c or whatever, depending on what heat is drawn from it.

So the boiler has to be sending water out above 60c to the cylinder for the water in the cylinder to reach the desired temperature.
 
G

Goldspoon

The water in the cylinder takes heat from the coil and when that body of water( the water that comes out the hot tap) is up to temp (60c) the stat then tells the valve to close.

I understand this. So stat on cylinder (60 in our case) determines temp of stored hot water. So what does the HW setting on the boiler do? Perhaps I am missing something here... but you verified that water going thru coil is same as determined by CH setting on boiler so if I set the little image of a tap on the boiler to 44 then what does that affect?
 
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What is the exact model of the boiler?

Is it a combi with a DHW cylinder attached?
 

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