Flow temperature on Greenstar junior

[D_Hailsham]

Quite so.

But that's making an assumption of 30 kW of rads.

This is a smallish 3-bed mid terraced house with a heat load of perhaps 8-9 kW which is very small for a 24 kW boiler.

I was just replying to your request that I explained how I calculated the temperatures when 30kW of rads is connected to a 24kW boiler. (At least that's what I thought you were asking.)

As for the OP's problem, I have to admit that I missed the bit where he said the house was well insulated etc and agree that he probably needs less than 10kW to heat it. Could his problem be caused by too large a boiler (heatingwise), so it is continually cycling - even when heating the house from cold? Can the WB Juniors be range-rated?

 

[Agile]

My question was in relation to the OP's situation.

A 24 kW boiler should easily manage a heating load of 8 -10 kW with no problem.

Working and set correctly it should also achieve about 80 C with less than 50% of its rated power.

BUT many boilers will not achieve an 80 C flow when the heating load is close to the maximum. That is due to their design. Or rather what I would call a design deficiency!

Tony

 

[vansbest]

Hi again, I took readings to-day over a 2 minute period and calculated the heat output to be 13.889 kW. Checked this on my i pad using an app from Ideal boilers and got the same result. Over 2 mins consumption was 43 units. Supply to boiler is 22mm throughout and tested using the suggestion of watching the hob flame when the boiler was on and hot water was called for. There was no change in the burner flame. any ideas?

 

[D_Hailsham]

Hi again, I took readings to-day over a 2 minute period and calculated the heat output to be 13.889 kW.

If that is based on meter readings, it is the heat input. The output is about 13.5kW.

That does suggest that the lowNox plug has been installed. Perhaps the installer did a heat loss calculation based on an outside temp of -1C, which came out to less than 13kW, so he thought the lowNox plug would be OK. He forgot that if the outside temperature dropped significantly, e.g -10C, the 13kW would no longer be adequate.

13.5kW with temps of 67/57 would be correct for 17kW of rads.

 

[vansbest]

Hi, i have posted responses but they seem to have got lost in the ether. I did a boiler rating calculation . This indicated 12kw input. I have taken room measurements, rads and calculate the radiator output to be 6372kW and using various on-line calculators the heat loss works out at 5295 kW. Would this explain the boiler flow and return temperatures I have recorded? And what should/ could I do to increase the temperature and allow me to reduce the boiler setting.
thanks for any advice.