oil boiler cycling

[frpcraig]

Hi All,great forum ,hope you can help?
I have an old camray compact 50/70 oil boiler, with a rdl g2-sx burner.
It has been serviced every 2 years by the same guy.
The time for the service seemed to be short so I did some investigating myself.
I removed the burner and hacked off 1/4 inch of carbon build up in the chamber.
He hoovered it each time?
The end result is now the rads/hot water now heat up much more quickly and reach a decent temp.
The down side is the boiler now short cycles.££££££!
The boiler runs 11 rads and a hot water tank.
If I put on only the hot water there is no short cycling.
I have replaced a defective roomstat and a defective 2 way motorised valve.
The system appears basic to say the least.
There is only one motorised valve to switch off the ch and a tap to isolate the hw tank (with no tank stat)
The boiler will run for a while until it reaches temp then cycle 3 mins on 3 mins off when asked for ch and hw.
The oil pump runs standard as far as I know and the nozzle is 0.65 60 W.
Do you think running the max size nozzle is causing the short cycling and I should drop down to a 0.40 nozzle to keep the burner on for longer.
With the same set up it seemed to run ok before I cleaned the chamber properly, is the boiler oversize??
Many thanks,

 

[frpcraig]

Thanks for the replies.
Bunker the rads both upstairs and downstairs all heat up to temp in 20 mins,
If I turn the boiler stat down it comes up to temp quicker then short cycles, if I turn up the boiler stat it takes a bit longer to get to temp then short cycles.
If I go from a 0.65 to a 0.4 I will reduce my gph by 37% rather than halving it as you mentioned.
Riellos spec sheet for my burner says you can run between a 0.4 and a 0.65 nozzle with the same pump pressure.

Lame plumber, if you re-read my posts I have always used a registered engineer, hence my issues!.

Peteheat, thanks again for your comments.
As mentioned I will get a stack temp ,co2 etc analysis done for sure.
What I object to is paying hundreds of pounds a year for an engineer not to service my boiler properly.
I am quite capable off scraping crap off the inside of my boiler if the engineer doesn't
I have found nozzle containers that vary from 0.4 to 0.65 in the case of my boiler.
I think my'engineer' has put bigger nozzles in over the years to combat the inefficient coked up chamber.
Best, thanks for your reply,
The boiler is sited in the downstairs toilet with a rad in it.No underground pipes
Most of the rads are singles and little.
I have no need to run the hw tank and the rads at the same time.
Cheers
Craig

 

[Bunker]

If I go from a 0.65 to a 0.4 I will reduce my gph by 37% rather than halving it as you mentioned.

Not talking about gph, talking about output Kws - the output on a .65 compared to a .4 is almost exactly halved at the same pressure, still you obviously know best....Im out.

 

[SimonG]

Hundreds of pounds a year on servicing? Think I need to come down and work in your area.

It's surprising just bhow quick an oil boiler will fill with crap when something goes wrong.

Spec sheets will tell you nothing but data from bench mounted burners running in ideal 'factory' settings. In reality you are going to have issues swapping bits without the correct gear.

What we need is more people like yourself tinkering with oil boilers to ensure there are more fatalities. That way stricter legislation will brought in to bring oil into line with gas.

Stupid people will make it safer for all.

 

[lame plumber]

Lame plumber, if you re-read my posts I have always used a registered engineer, hence my issues!.


As mentioned I will get a stack temp ,co2 etc analysis done for sure.
What I object to is paying hundreds of pounds a year for an engineer not to service my boiler properly.
I am quite capable off scraping crap off the inside of my boiler if the engineer doesn't
I have found nozzle containers that vary from 0.4 to 0.65 in the case of my boiler.
I think my'engineer' has put bigger nozzles in over the years to combat the inefficient coked up chamber.

Having a boiler serviced every 2 years isnt enough to keep it running efficiently. if your paying hundereds of pounds a year for servicing and having to decoke your boiler, then prehaps you ought to reconsider if he knows what hes doing, you obviously dont if your assuming he's changing nozzle size to combat soot build up. more likely it's all he had in his nozzle selection at the time! you really should find a decent registered techie to do a decent job and for your information an hour and a half is quite normal for anaverage service, more for something like your boiler.

 

[dontknowitall]

Is there a by-pass fitted?

 

[frpcraig]

Thanks again,
Look please stop shouting at me and telling me I am an idiot.
You don't know my background.
I do understand the dangers involved ,I am just fed up of paying for poor service.
I heat the house with coal fires and have electric showers etc so I am not at the mercy of the boiler.
I don't run the boiler other than tests when the house is empty.
Tonight i fitted the 0.4 nozzle and the burner runs continuously for 1 hour 20 mins, you may think that is insane but I know that the boiler does not short cycle running a smaller nozzle and runs on a 4 minute cycle on the 0.65 nozzle.
In fact the boiler has now shut off after reaching roomstat temp (this minute).
That took 1 hour and 20 mins.
Berfor with the 0.65 nozzle it would heat up to temp in 20 mins and short cycle.
I am timing now on the 0.4 nozzle to see when it starts up again.
Pete you mentioned the longer run time issue running a 0.4 nozzle,do you think a 1 hour 20 min run time from cold is ok.
Cheers
Craig

 

[SimonG]

But you are.

 

[lame plumber]

no one is shouting but you are being rather stupid.

 

[frpcraig]

Ok then , last question,
What would everyone consider to be an acceptable/efficient cycle time?
Thanks

 

[lame plumber]

if its heating up quickly on a larger nozzle and then short cycling something is wrong with the thermostats somewhere, just because a very small nozzle takes longer for it to heat the whole system and then turn off doesnt mean its right. It only takes 10 mins to warm my rads and the boiler doesnt short cycle thereafter, you have a problem thats resolvable but needs looking at properly, advice now given why not take it for all our sakes.

 

[frpcraig]

Thanks lameplumber ,yes I have a new engineer booked in for next week.
What do you think an efficient cycling time is?
Thanks

 

[lame plumber]

if you mean how long to warm rads 10 mins reasonable and then your boiler should cycle on and off as required, and it will take however long it takes to cycle on and off, but obviosly not on off on off every minute or so.

 

[frpcraig]

I just want a rough idea lameplumber.
!0 mins off 10 mins on , 20 mins /30 mins etc.
A ballpark would be good,
I have read an oil burner comes to max eff, after 18 mins??
Thanks,

 

[lame plumber]

it will take at least 10 mins to reach peak efficiency as a boiler with correct flue temps etc, but then of course it will cycle on and off as req by need to heat return temp of water. best advice to you is to stop reading and trying to comprehend oil and burner manuals and just refer to the owners operating guide.

 

[dontknowitall]

Is there a by-pass fitted?

Thanks again,
Look please stop shouting at me and telling me I am an idiot.
You don't know my background.
....

I wasn't!!! If there is no by-pass fitted then it might short cycle. If there is a by-pass fitted then it could just be a case of adjusting the gate valve.