Grant Euroflame Condensing Oil Boiler Temperatures

6 Jan 2017
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United Kingdom
Hi Folks,

I have read a lot of posts regarding operating temperatures and return temperatures, but I still need a bit of help.

My house has oversized radiators and grundfos alpha 2 pump.

I gather from the Grant UK manual that they recommend that the flow should be around 70 degrees and return 50 degrees.

I have tried setting the boiler at its lowest operating temperature and the house heats very well. I have invested in pipe stats to help read the return and flow temperatures. I really don't know if they are working properly as the flow was around 52 and the return said around 35.
The Grant manual states not to run the system with a return temperature of less than 40 degrees. Not really sure why, would this cause problems.

I notice that during the warm up process the boiler produces a good stream of condensate but this eventually slows away down as the system gets up to temperature even at the boilers lowest setting. So going by my pipe stats reporting only 35 degree return I decided to follow the Grant manual and crank up the boilers thermostat so that it would produce a 66 degree flow and 52 degree return (roughly). I noticed that still there was not much sign of any noticeable condensate. Grant tech told me that there should be a steady stream or drips if the boiler is in condensing mode. I assumed it was not and the radiators felt very hot to touch.

Do you think it is better for me to run the boiler at its lowest water temperature as it heats the house well at that setting or would I be better to crank it up and have it firing longer?

The house is well insulated and the boiler is a Grant euroflame 50/70 non modulating condensing model. Our hot water tank is heated by a solar i boost to above 60 degrees regularly so that would not cause any problem running at lower temps. All rads have trvs.

Any advice would be much appreciated. I really want the system to be operating at its peak efficiency and i am willing to try anything, including finding the best way to accurately read the temps of the 22mm copper flow and returns.

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The only accurate way to measure pipe temperatures is with a contact K-type thermocouple meter.

I am not sure that it is quite as importance as you seem to think to run the boiler at particular temperatures.

Run it as low as you can but aim for the 40°C return temp if that's what Grant want. You should also be aiming for a 20°C difference between the flow and return temps, so 60 flow and 40 return. Because they can't modulate, oil boilers will never condense 100% of the time, but it sounds like yours is set up much better than most
It's the way grants are built and materials used if the return temp is not above 40-50 degrees you will get corrosion and I mean corrosion like you have never seen it all starts with temp below 50 what happens is you get dew point forming in the combustion chamber which when mixed with the flue gasses turns acidic and there we go it rots and very fast too.So keep the return high or else you may be changing your boiler like the chap in tolsta near me he would not listen to me and three years later back blew out of boiler rotten as an old carrot.Bob
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Thanks for the help Guys. Much appreciated.

I will look into the k-type. Just a quick update.

I had read about pump speeds also and tried putting the pump onto speed number 3 (alpha 2) rather low wattage compared to my old noisy pump. And low and behold a good stream of condensate trickles out as the boiler warms up. Then when system is at temperature it slows to just dripping. Much better than nothing coming out.

It is interesting that you say non modulating boilers won't condense 100% of the time so I assume that my system is pretty much running at a good efficiency now that I see condensate most of the time. The oil boiler takes around 15 minutes to get up to temperature and then cycles on for around 4 minutes and stays off for around 3.5 - 4 minutes. Hopefully a good sign that when running the condensate drips out.

I have an infrared themometer gun I picked up off eBay. It is not good for telling the temperature of metal but it is saying that my rads are around 54 degrees, they feel hotter but I will try to source a better temperature reader just out of curiosity. I had wondered if it wasn't far away as the pipe stat (another cheapy from ebay) reports a return temperature of 35 degrees or thereabouts. But I have a funny feeling it is under-reporting. When I shine the themometer gun onto the powder coated alpha 2 it reads 40 - 42 degrees.

Anyway I think it is running much more as expected now. Do any of you know if it will do any harm if my return temperature is slightly less than what Grant's stated 40 degrees?

But bottom line - The pump on setting 3 got my system to start producing condensate so maybe worth a try if anyone else is having the same trouble.

Cheers Guys :)
Hi Bob, just seeing this now after i already posted. Thanks for this info, I will get a proper stat and make sure it is what Grant recommend. Boilers are not cheap so I certainly don't want to be buying a new one in 3 years time. Cheers
I have a standard efficiency grant euroflame for 18 years now. Think I changed the motor capacitor in that time.
Great wee boiler. Been serviced about once in all. I check the pressures now and then.
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Yes ok as long as you look after them the standard efficiency boilers didn't give much trouble and as they never condensed no acid to watch I'd get the flue gas checked every year just to watch the efficiency doesn't drop too much if it does get a new nozzle fitted.Bob
I turned it up a little Bob so that the rads are now 60 degrees. I have ordered a ktype thermocouple meter to balance and keep an eye on the system. That way I can be 100% sure all is running at its best and no corrosion. Thanks for the tip! I will let you know how I get on

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