Lukewarm Radiators

[Keepinghouse]

Hi guys, any help would be greatly appreciated.
I have a riello rdb oil boiler. We only moved into the house a few months ago and have noticed the radiators are never hot- just lukewarm. All the radiators are the same. The boiler looks relatively new. I have the thermostat on the boiler turned to max but it does not seem to make a difference.
What should I do?
I should add that we have plenty hot water due to an immersion heater.

 

[terryplumb]

Get an engineer in to check it out ,if you have turned the boiler stat to max there is something amiss.

 

[Johntheo5]

Hi guys, any help would be greatly appreciated.
I have a riello rdb oil boiler. We only moved into the house a few months ago and have noticed the radiators are never hot- just lukewarm. All the radiators are the same. The boiler looks relatively new. I have the thermostat on the boiler turned to max but it does not seem to make a difference.
What should I do?
I should add that we have plenty hot water due to an immersion heater.

If you can locate the circ pump, post its make/model/mode/setting, it may be close to the boiler or upstairs in the airing cupboard if you have a Y system with a 3 port mid position valve.

 

[Keepinghouse]

Thanks for the reply guys, this is what I have. I checked the copper pipes and they are warm but definitely not hot

 

[Johntheo5]

If the boiler is only firing for a few minutes or less then looks like a circulation problem.
Can you hear the pump running?, you can remove the (vent) screw on the pump front, a small trickle of water will come out but nothing to worry about, you can then see if the pump shaft is turning.
If you feel the flow pipe between the boiler and pump is it very hot??.

 

[Keepinghouse]

If the boiler is only firing for a few minutes or less then looks like a circulation problem.
Can you hear the pump running?, you can remove the (vent) screw on the pump front, a small trickle of water will come out but nothing to worry about, you can then see if the pump shaft is turning.
If you feel the flow pipe between the boiler and pump is it very hot??.

boiler is firing continuously. pump is running- I just opened it , small trickle of water as you say and I can see the shaft turning. Speed can be adjusted too. Flow pipe between boiler and pump is a little more than warm but not hot and definitely not very hot.

 

[Deleted member 294929]

Check that any valves in the area of the boiler are fully open and maybe a powerflush.

 

[Deleted member 294929]

It looks to be a rubbish installation, I'd get an oil engineer to look it over for you.

 

[Johntheo5]

boiler is firing continuously. pump is running- I just opened it , small trickle of water as you say and I can see the shaft turning. Speed can be adjusted too. Flow pipe between boiler and pump is a little more than warm but not hot and definitely not very hot.

Looks like something in the combustion side, a 20 or 30kw oilf fired boiler doesn't modulate so can't see it firing continuously without heating the water to cut out point, can you see a flame through the viewing port?.

 

[Keepinghouse]

had a plumber out today- they reduced the rate of output flow and now things are heating up- he said that the boiler wasnt heating the water fast enough to keep up with the flow.

 

[Johntheo5]

had a plumber out today- they reduced the rate of output flow and now things are heating up- he said that the boiler wasnt heating the water fast enough to keep up with the flow.

Must be a very low output boiler.
How many rads?, doubles & singles.
What is the make/model of the boiler? if there is a label on the boiler, post a photo of it.
Also model of Grundfos pump + setting.

 

[Keepinghouse]

Must be a very low output boiler.
How many rads?, doubles & singles.
What is the make/model of the boiler? if there is a label on the boiler, post a photo of it.
Also model of Grundfos pump + setting.

When I say plumber I meant to say the plumber sent his two apprentices..
25 radiators- mostly doubles.
Output from the boiler directly is very hot but the return feels fairly cool. I would assume boiler would switch off once the return reaches a certain temperature?

 

[Johntheo5]

Ok, assume 25 rads have a total outpout of ~ 32kw.
Boiler max output is 70, 000BTU, 20.5 say 21kw.
Burner output can give, depending on jet size, output 14.3kw to 26.3kw, boiler output ~ 13kw to 23.7kw.
I would get someone to check the nozzle size is sufficient to give the maximum boiler output of 21kw as a start.
Boiler is undersized, the rads would need flow/return temps of 75C/65C to emit their full rated output.
If the boiler flow temp is set to 65C (or equivalent on the index) and the pump speed set to lowest (6M) then the boiler should get up to that temperature and then cut out as the demand will be ~ 20kw, it may take 30/40 minutes to achieve this, if it doesnt then I would suspect the jet sizing.
Yes the burner should switch off once the return temperature in the above scenario reaces ~ 45 to 50C because the temperature rise dT through the boiler should be ~ 20C or a less, if the dT is 15C then the burner will switch off (at a flow temperature of 65C) when the return temperature reaches 50C.
If your system is zoned then just try heating 10 or 12 rads, a 21kw boiler should then have no problem in reaching its target temp and cutting out.

You can check/change pump speeds yourself, try minimum, if not allready set.