Worcester heatslave - flame stalling ??

[Heatslave]

Evening all,

After taking my Worcester Heatslave out for a welded leak fix on the boiler, it has been making a strange noise since reinstalation.

It is definately inside the burner that is making the noise. To best describe it is to say it sounds like it is "stalling", as if the flame is going off then on.

As soon as I remove the burner outer cover the noise stops and it sounds like a Worcester Heatslave should sound. Put the burner cover back on and it starts "stalling" again.

The only two things I think it could be is a blocked flue or fuel starvation.

The reason I don't think it's a blocked flue is that when I take the flue top cover off (at the flue itself) there is no difference in noise.

The flexible pipes to and from the oil pump are new after market ones and are much longer than the standard Worcester ones. I thought they may be getting pinched when I put the burner cover on and stopping fuel flow, but it is difficult to replicate this.


Any other thoughts ??

 

[wilhelm]

sounds like flue gasses mixing with inlet air. Sure you aint distrurbed flu ?
and i presume we talking about silver coloured box type cover?
I must admit i fit 600mm fuel lines on them tw£ts, cos youre right, there aint much room

So could be fuel/kinking prob.

 

[Heatslave]

No I don't think the flue gases are mixing as I used fire cement on the flue ring as recommended.

It feels very much like an air flow problem. With the silver burner cover released from it's locking studs by about an inch, the noise stops, as if the burner is getting enough air. As soon as I seal the cover the stalling / surging starts again, as if the burner isn't getting enough air.

I've got to point out I'm not a heating specialist, but I assume there is a fan in the burner to mix the fuel / air supply. It sounds like the fan is stalling.

 

[wilhelm]

well, what you describe sounds like flue gasses mixing with air.

trust me

you need to get someone in really to check combustion.

 

[Heatslave]

Wilhelm,

I'll take your word for it.

Many thanks for the free advice, much appreciated

regards,
HS

 

[OilLecky]

HeatSlave.
Can you tell us what size Heatslave boiler you have i.e. 12/14 or 15/19 etc. Is it a combi, does it have a conventional flue or a balanced flue and what is the burner exactly? There is an identification plate on them. Electro-Oil B9A, B9B or B11 perhaps?
It does sound like you have an air supply problem but I cannot identify this "Silver Burner cover" or the "locking studs". Can you give a bit more of a description or if you have a photo editor, a picy with an arrow saying "this cover".

 

[Heatslave]

Hi OilLecky,

It's a Heatslave 15/19 oil fired combi with a room sealed balanced flue.

The burner cover is a metal box you remove to access the oil pump and burner.

By taking the burner cover off you are allowing air from inside the house to get to the burner. By putting the burner cover back on you are creating the roomseal and the air is drawn in from the balanced flue.

Does that make it any clearer.

 

[oilman]

HeatSlave.
Can you tell us what size Heatslave boiler you have i.e. 12/14 or 15/19 etc. Is it a combi,

It must be a combi, it's a Heatslave. Non-combies are Danesmoor.

 

[OilLecky]

You are of course correct OIlman. Its a combi.
I am with you now Heatslave. The cover is as per a balanced flue installation. You have virtually cracked it yourself. With the cover fitted, the burner is drawing air from the balanced flue and with the cover removed or loose, it is drawing air from the room. Check that the balanced flue air inlet duct has not got blocked during the repair. It is either blocked or there is a path for the gases from the flue outlet into the air inlet duct. If necessary, take the flue to pieces again.

You are correct. The burner has a motor in that drives a fan which sucks air in and blows it over the fuel nozzle. The motor also drives the fuel pump. Somehow the fan is being gagged.

 

[Heatslave]

Thanks very much for the advice, much appreciated

Listening from outside the house close to the flue exit it sounds like a popping (banging is too harsh a word for it), a bit like a car misfiring, if you know what I mean ??

 

[OilLecky]

The burner is going out (due to lack of oxygen) the photo-cell sees this and relights the burner by starting the ignition sequence again "pop"! This repeats itself so that is what you can hear. Check your air inlet in the balanced flue installation. The flue exhaust gases should exit via the centre pipe and the fresh air should enter the burner by the outer pipe. Make sure that the outer is clear all the way to the inlet under the burner. (See below.) If it is, then the exhaust gases must be getting into the air intake.
If you haven't twigged yet, the air actually arrives at the burner at the lower edge of the box that holds the burner cover. Remove the burner cover and burner and make sure that this narrow slot is not full of debris! Good Luck.
I'm off on a job now will check back later this afternoon.