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Discuss Worcester danesmoor 20-25 oil boiler low water temperature. in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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Joe Drakeford

Hi everyone

I have an oil fired boiler in sealed system supplying underfloor heating and a megaflow hot water cylinder, the system is sealed and controlled by 2 motorised valves. The underfloor heating manifold is from IHS and the temperature is controlled / reduced here by a temp / flow control valve, not a mixing valve. I usually run the underfloor at approx 40 deg C, but when I turned up the temp to 50 deg C, I could not achieve this, firstly I thought it was a problem with temperature control valve at the manifold, removed this nothing wrong. I then fitted a clamp on temp gauge at the boiler outlet, I get around 50 deg C with the boiler turned up to the mid position on the dial (it cuts out at this setting after a while), full up and it eventually reach 60 deg C, but after about half an hour or so it didn't cut out. According to the manual it operates between 55 and 82 deg C if I remember right.
Oil nozzle has been changed and combustion has been checked with flue gas analyser.

I wondered if the thermostat was faulty but it seems like the boiler is running for fairly long periods of time, would have suspected the boiler to cut out sooner if the stat was stopping the boiler at a lower temp??

Anybodies input would be appreciated

Regards, Joe
 
What was the oil pressure, co2, excess air and flue gas temp?


Hi, thanks for the reply

I'm away from home but I do have a print out from the analyser at home,
I know the fuel pressure was 105 PSI, don't remember the other values but
will get back with these.
 
Hi
The print out isn't all that clear but it looks like:

CO2: 11,2
FLUE GAS TEMP: 188,3
EXCESS AIR: 38,4
FUEL PRESS: 105 PSI

Some other figures from the print out:
CO: 61
INLET 12,4
NET 175,4
EFFICIENCY: 92,3

Hope this helps, thanks
 
And whats the nozzle - should be a 75 80 EH if set up to standard MI but details are printed on the label.
 
It's a 0.75 80 EH according to the manual but maybe would need to double check the actual nozzle.
You say the details are printed on the label, which label do you mean?
 
I don't think its on the print out, but it was checked with a gauge. I did double check the nozzle about a week or so ago and it was the right one as far as I remember, unless its a faulty one.
away from home just now so not able to take it out again and check.
 
Hmm.... Bit strange, I personally wouldn't of thought it would be the combustion, you could have some settings quite a way out and it would still produce hot water. Is the water pump actually getting rid of the water out the boiler?
How hot does the main jacket feel behind all the insulation?
The first thing I would do is whack a thermistor probe on my analyser and stick it in the pocket where the control stat goes, then all the other pockets and check what temp they are saying.
But definitely sounds like a water pump issue or blockage of some sort.
 
If you are still unsure, turn the stat down low and fire it all up, when it reaches temp, turn stat up a bit more, do it in slow increments until up full, then you know stat works and you have hot water.
 
If you are still unsure, turn the stat down low and fire it all up, when it reaches temp, turn stat up a bit more, do it in slow increments until up full, then you know stat works and you have hot water.

Thanks for your input, I have been through the possibility of air locks and pump. Changed the pump as I had a spare but made no difference. I'm thinking about checking the inside of the boiler walls and giving them a good wire brushing in case there is a build up of soot in their reducing the heat transfer. I'm away until next Tuesday so will look when I get home and let you know how I get on!
 
Any further on this?

would have to be a huge amount of soot to prevent that from working, so surely the photocell would've kicked in by that point?

Sounds like a dodgy stat to me, had a few on Heatslaves but normally the other way round. Everything to do with the burner sounds right so doesn't leave a lot!

Whats the difference of when the stat clicks on and clicks off as you turn it on the front of the boiler? Sometimes when they start to go you can have a 90° turn of the stat between the two.
 
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