Help needed on oil boiler

[Woodman133]

Hi,
I have a Grant vortex eco oil boiler which as a Riello RDB burner. My problem is the boiler keeps cutting out. Once up to temperature the boiler runs for about 2-3 minutes then cuts out for about 3 minutes before starting up again. The pump keeps running during the cut out time.
From what I can make out, it is either the high temperature thermostat on the boiler or the boiler is set too high and the pump therefore does not take the heat away quickly enough. The boiler is about two years old as is the pump - a Grundfoss. The pump is set on highest speed, and there is always at least one radiator which has it's TRV set to fullly open.

Does anyone have any ideas on this? If the boiler really is set too high, is it possible for it to be adjusted by a DIY person or is this a plumber job? There is a dial on ths front of the burner, currently set to 3. Can I adjust the heat output by altering this, and will doing so change the burn mixture? Would this be a possible solution to my problem. The burner is rated from 19.2 - 33.5 kW so it seems there is a wide range of adjustment.

K

 

[lostinthelight]

Whats the difference in temperature between the flow and return pipes at the boiler?
litl

 

[oldbutnotdead]

Are the radiators getting hot? (especially any on the ground floor). If the system is 2 years old, was working properly and now isn't and no-one has been fiddling then I'd be getting suspicious of (a) the pump (b) any motorised valves in the system (and yes they should be wired to interlock the pump but maybe they haven't been) (c) is there any water in the system.

As far as I know the burn rate is not a user adjustable setting- the control on the front just determines what temperature the boiler will cut out at so increasing that may reduce the cycling provided there is actually flow in the system.

 

[Agile]

With a heat output of 19-33 kW I would expect it to cycle on/off because the property is unlikely to be able to absorb all that power.

A typical modern 4 bed detached house only needs about 15 kW or less.

Older properties with solid walls somewhat more.

So if the rads are getting up to temperature then I would expect it to be working totally correctly!

The "on" time could usefully be extended if you had the boiler output power setting reduced at the next service.

As a guide the FAQ have formulae for working out an approximate heat loss for the property. They are all somewhat approximate. I would make a very good guess from the floor area and knowledge of the wall construction and loft insulation.

Tony

 

[Woodman133]

Hi guys, and thanks for taking the time to reply. Just to clarify, the system is a conventional one ( not combi) and the building is a barn conversion. There are two bedrooms and a bathroom upstairs but now that the kids have left home the rads upstairs are set to low or off on the TRVs.
Downstairs is a large hallway where the thermostat is, and a lounge kitchen diner with high vaulted ceiling that takes a lot of heating. Also a couple more bedrooms, so the main load on the heating is the lounge erc and this is not usually really warm in cold weather - the rads only just cope.

To answer the questions, flow and return pipes are both hot but I don't know the exact temperature difference. Return is too hot to touch anyway.
The rads all get hot upstairs and downstairs, and they are hot all over. There was an occasional gurgle of air in the system but I think I have bled it all out now.
I am not sure how long this has been happening. The boiler was serviced around last March but wasn't then used until this winter - we don't run it in the summer because we have solar panels which divert excess energy to the immersion heater. So this could have been an issue since then.
There are 2 controls on the front of the boiler. One is the temperature which is for the user to control. The other one which I was asking about needs to be set using a screwdriver and is on the burner itself.

Any further ideas?

K

 

[oldbutnotdead]

I'd be leaving the screwdriver setting alone unless the operating manual tells you what it does- oil burners can be finicky little sods. Have you done a heat loss calc on the high ceiling room- may just be the rad is a bit undersized.

And the cycling may very well be exacerbated by having the kids rooms at tickover- try running all the rads at full on the trvs and see what happens (don't start messing with lockshields, you could upset the system balance).

 

[muggles]

Don't try to adjust it yourself - ink order to do that correctly you need a new nozzle, a pump pressure gauge and a flue gas analyser. Incorrectly adjusted oil boilers will produce smoke and soot which can take hours to clean out again

The dial with the numbers on it adjusts the air setting, and adjusting this alone will create soot but no change in power

 

[Agile]

Rather than calculating the heat loss, a more relevant figure would be the rad heat output as it sounds as if they are not large enough to match the building heat loss.

Compare the sizes with a catalogue of rads.

Quite clearly to me the boiler is just simply over powered for the heating load. That will still be the case even if the boiler had been down rated to 19 kW.

Oil boilers don't modulate and their output is managed by cycling on and off just as yours is doing. All totally normal.

Tony

 

[oilboffin]

Is the boiler still not under warranty