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,

 

[lame plumber]

oil boilers require servicing annually to work efficiently for a start. all the cdarbon was probably masking a stat that is now able to operate and is probably locking out to cause short cycling or you fiddling has cocked up the controls side, basically you need to get it serviced ,set up and checked. to be efficient you need a hw cyl stat and another motorised valve on the system, then you might save some money

 

[frpcraig]

Hi thanks for the quick reply!
As I mentioned the boiler servicing was not up to scratch.
The boiler stat and the high limit stat are in pockets above the tank and have no carbon issues.
There is no 'locking out' of stats.
The stats operate correctly.
'fiddling has cocked up the control side'
Can you elaborate??
Many thanks

 

[frpcraig]

Lame plumber,
Does that make sense??

 

[lame plumber]

might well be one of the boiler stats is now getting some heat now all the carbon gone and its failing and causing the short cycling

 

[frpcraig]

Thanks lame plumber,
As I have said, the stat probes are above the heat chamber so they never had any carbon build up.
They all work to spec.
There is one high limit stat working correctly and the boiler stat also working correctly.
The boiler is heating the tank much more efficiently now I have scrapped all carbon off the inside.
No other changes.
All as before this.
Any more ideas???

 

[lame plumber]

no but the burner chamber was! stopping heat reaching them, get someone in who can a service it, b set it up and then c fault find it

 

[peteheat]

Take a look at the OFTEC website, there is a section where you put in your post code and get a list of competent technicians for your area.

Carbon build up is not a good sign, depends on what you are burning diesel or kerosene (not familiar with that brand) if you change the nozzle you will need the oil pressure re-set a smoke pump and a flue gas analyser to be sure the boiler is working properly.

 

[frpcraig]

Thanks peteheat, I will definitely be getting a full system analysis done.
The carbon build up is a result of many years of improper servicing, no wire brushing, no scraping etc.
I have done this job myself and it transformed the boiler from producing lukewarm water to hot water.
The burner oil pressure is set to 8 bar and can run nozzles between 0.4 up to 0.85 without the pressure needing to be changed.
My thoughts were as the boiler is now heating properly the 0.65 nozzle fitted is too large for my needs causing short cycling and too much heat loss through the exit, hence my thoughts on fitting a smaller nozzle.
What do you think?
Thanks
Craig

 

[peteheat]

Hi,

My thoughts are the first thing needed is to find out why there was a carbon build up, which is why I was asking which fuel is being used, a properly set up burner will not build up carbon deposits to any great extent.

Many people are surprised at how little it takes to kill off the efficiency of the boiler so your cleaning is allowing the boiler to do what it was designed to, exchange heat, so well done.

On older boilers the manufacturers instructions are nothing more than a guide, a starting place for the engineer to get the correct mix of fuel and air, equally if not more important is the type of nozzle fitted, a heavy carbon build up is often caused by the flame actually touching the steel inside the boiler, the caveat was "subject to local conditions".

You are correct in that the boiler may now be generating too much heat, equally it could be caused by an old pump not being able to dissipate the heat fast enough, another cause of cycling can be retrofitting heating controls.

If you fit a .4 nozzle without the necessary equipment to set up the burner you could end up with a boiler that is not capable of meeting the heat demand of the house a drop of .25 is a lot, maybe the boiler was sized for the house when it had single glazing, practically no insulation etc we can only assume the boiler did suit the house when it was installed

I suggest starting with the heat demand for the house by calculating the heat loss, that is what determines the size of the boiler and the nozzle needed, if the heat loss of the house has changed over the years you may find the figures justify upgrading the boiler to a new smaller efficient condensing boiler, oil is too expensive to be getting the figures wrong.

 

[frpcraig]

Great reply, thanks.It sounds like you know my house!!
All of the things you mention make sense.
We bought the house 10yrs ago.
It's a 300 year old farmhouse ,not flashy more of a do-er upper!
We have replaced most of the single pane windows with double glazing and insulated the loft also.
I put a new danfoss pump in last year (the red one) and that appears to be still ok.
I would love to put a new more efficient boiler in and it is on my 'to do list' but I haven't got a pot to p**s in at the minute.
When I fire up the boiler from cold I can get all the rads up to temp in 20 mins and then the cycling starts. Before I cleaned the chamber the rads never really got up to temperature.
When it cycles I reckon it is doubling the fuel usage (kerosene) so I run for 20 mins then switch it off till the rads cool down.
All the different size nozzles applicable to my burner seem to have the same spray angle so hopefully the flame isn't hitting the sides of the chamber.
When we moved in kerosene was 13p a litre so you could leave it on for fun!
At 60p it becomes serious!
I will have a look for heat loss calcs and try and work it out.
My small nozzle arrives tomorrow so i'll try it and let you know the results Pete.
Thanks again
Craig

 

[Bunker]

You say the stats are working fine, so surely if you turn the boiler stat (dial on the front - if it has one) it wont cycle, or at least will do less.
Please also tell us if all the rads get hot, upstairs and downstairs?
If you just stick a small nozzle in, youll be halving the output and ought to adjust the pump pressure to suit the combustion.

 

[lame plumber]

Great reply, thanks.It sounds like you know my house!!
All of the things you mention make sense.
We bought the house 10yrs ago.
It's a 300 year old farmhouse ,not flashy more of a do-er upper!
We have replaced most of the single pane windows with double glazing and insulated the loft also.
I put a new danfoss pump in last year (the red one) and that appears to be still ok.
I would love to put a new more efficient boiler in and it is on my 'to do list' but I haven't got a pot to p**s in at the minute.
When I fire up the boiler from cold I can get all the rads up to temp in 20 mins and then the cycling starts. Before I cleaned the chamber the rads never really got up to temperature.
When it cycles I reckon it is doubling the fuel usage (kerosene) so I run for 20 mins then switch it off till the rads cool down.
All the different size nozzles applicable to my burner seem to have the same spray angle so hopefully the flame isn't hitting the sides of the chamber.
When we moved in kerosene was 13p a litre so you could leave it on for fun!
At 60p it becomes serious!
I will have a look for heat loss calcs and try and work it out.
My small nozzle arrives tomorrow so i'll try it and let you know the results Pete.
Thanks again
Craig

fm what youve just said it seems you dont use an engineer to set up your boiler and thats probably half the problem. diy and boilers is stupid and dangerous and itll will have to take someone like yourself killing their family to force the government to make similar regulations to that of gas before fiddlers are made illegal, for good reason

 

[peteheat]

Hi Craig,

The drop in nozzle size is substantial, I expect you will still have a boiler wasting fuel as it will be trying very hard to get up to temperature, the opposite of your original problem (cycling) you will also be sending a lot of unburnt fuel into the atmosphere.

At 60p a litre you don't have to save a lot of fuel to justify the cost of employing a professional who has the right equipment to get you the best out of every drop of fuel.

Personally when money is tight I hate the thoughts of my limited resources being wasted.

I have to agree with lame plumber legislation is needed to ensure that consumers treat oil systems with the respect they deserve because at worst they can kill, they can also cause major damage to the environment when not properly maintained.

 

[Best]

Where is the boiler sited? If the pipes from it were underground, then severe heat loss can be a problem. If not then your boiler stat could be faulty.
Changing the nozzle to a very small one is nonsense. That output of boiler usually needs approx .6 nozzle. 11 rads (even smallish) & a hot cylinder will need that size of boiler output so do not lower it - have the nozzle replaced with proper size only. You haven't a clue tbh, needs an engineer to set it all up.

 

[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.

 

[peteheat]

Thanks for the replies.
Bunker the rads both upstairs and downstairs all heat up to temp in 20 mins,

About right.

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.

Reads exactly the opposite to what I would expect, what controls your boiler firing?

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.

Riello manufactured the burner not the boiler, it is the boiler manufacturer who spends the big money on R & D to ensure the correct burner, nozzle and settings are used to achieve the most efficient performance.

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.

Far as I know from earlier posts I'm probably one of the most expensive service engineers who posts here, allowing for currency exchange rates I would be charging circa £100.00 for an oil boiler service.

I want my customers back again next year so if there is a problem with a job I do I want to know about it, I understand most who post here have a similar policy.

With respect I suggest you use a new service engineer / technician preferably one with a plumbing back ground.


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.

The burner can use nozzles in that range, that does not mean they suit the boiler in fact .65 is only part of the nozzle data.

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

You mention in a later post that it is now taking a continuous 80 minutes to achieve the same temperature the larger nozzle achieved in 20 minutes, the basic maths should be telling you all the advice you received was correct, you are using more oil with the smaller nozzle.

To answer your last question, the cycle time should be directly related to the heat loss of the building.

Nobody is calling you stupid we are trying to help by posting a few lines (I touch type with one finger) after we have completed a fairly hard days work, it is not always possible to trouble shoot a boiler problem without being in front of it.

Sorry I can't be of more help.

 

[frpcraig]

Thanks everyone, I have put the original nozzle back in the burner and promise to stop fiddling!
dontknowitall, I have found another manual red valve in the bathroom. It was wide open.
When I close it the boiler gets very hot then shuts down. There doesn't appear to be any short cycling when the valve is shut.
The boiler water temp stays hot for ages.
If I open the valve the boiler water temp (in the boiler tank) loses heat at the rate of 15 degrees celsius in 3 mins!
Is this the bypass valve you talked of?
Thanks
Craig

 

[Best]

Is this a red headed valve (probably a gate valve?) at a copper cylinder?
If so, then could be there to balance the flow through the heating coil.

 

[frpcraig]

Thanks Best, it is a red headed valve ,it is in the hw tank area.
One connection to it goes up into the loft, one connection seems to connect to the top of the hw cylinder and the ( a smaller pipe) goes to the hot water tap in the bathroom sink???
I may be wrong but that's what it looks like.
I've done some more tests and with the valve open the boiler gets up to temp then cycles often at about 70 degrees according to the boilerstat.
When I fully close it the boiler tank temp hits 95 degrees but does not short cycle.
Any ideas??
Cheers
Craig
If I turn the valve shut the boiler tank temp gets up to 90 degrees

 

[frpcraig]

When I say the tank temp hits 90 degrees I mean the top , the bottom is 70 degrees if that helps??