vokera 20 80 flowmatic - hot water very hot then burner stop

[raptor4109]

hi, I've been doing some reading of this forum and wondered if someone could help.

As subject I have a 20-80 flowmatic and it's pretty much been serviced every year bar a miss 2 winters ago (couldn't get an engineer as servicing boilers was less money than fixing broken ones on call out rates) and currently it's under British Gas Homecare contract

Anyway the problem:
turn on the hot water and the water gets very hot, scalding hot then the burner will stop (pilot light still on), cold water flows out the tap then the burner kicks in and the water temperature climbs again to scalding then the burner cuts out. repeat until hot tap turned off.

Lowering the thermostat control for the hot water merely gets the burner to stop sooner but it's the same hot cold hot pattern. Last call out from BG the engineer said, meh it's an old boiler likely full of sediment. It's old yes but, when bleeding the radiators it's clean water coming out.. Any ideas folks?

<sorry for long first post but figured more info better than no info.. >

 

[nickso]

I feel a recall coming on for that BG guy

 

[DP]

In Glasgow, I offer to repair/ service, Areas around glasgow, say 50 mile radius same rule applies.

If you were outside my operational zone, could provide assistance to visiting engineer.

What I have to say is, you have a good boiler that needs a good engineer to service and fix. Fault you have should not be a problem for someone who knows what they are doing. A young wipper snapper will be all thumbs I would imagine.

Nickso, I think the BG guy will be returning to say parts no longer available so it is time for a new boiler. What do you think?

 

[dcawkwell]

BG are truly hopeless. Did he even get his multimeter out to find the problem?
You have most likely a simple fault.
Give BG the push and use the services of a local engineer
who could have fixed this.

I would be checking the hot water thermistor for a start.

Good grief.

 

[nickso]

.

Nickso, I think the BG guy will be returning to say parts no longer available so it is time for a new boiler. What do you think?

Well he is techinically not wrong, some parts are NLA but whether it's the ones he needs to replace or not is another matter.

 

[45yearsagasman]

I would be checking the hot water thermistor for a start.

Where would that be on a 20-80 Flomatic?

 

[DP]

I would be checking the hot water thermistor for a start

Echo

 

[raptor4109]

aye the BG guy was an electrician how asked me to turn on a hot tap then he turned up the water pressure and left saying the system needed flushing but would likely break due to the pressure of the flush.. I reckon another call out is needed but that's half a day of my time wasted I mean the damn thing works it's juts a little too hot and I'm worried the extra heat generated will break something else in the boiler. I checked again last night and the burner (to my mind) runs full pelt when the hot tap is on, no regulation which i believe it should do to balance the water temp (or am I talking rollicks?)

I'm not one for prodding in gas boilers so not sure where to look - I do know all the cover screws are missing so easy enough to get into it

DP - I'm based in glasgow city centre, just off Bath Street

 

[DP]

This is one boiler that rarely suffers from sedimentation, so power flush is out of the window as far as I am concerned.

If the pressure were indeed low (can be down to nearly 0.5bar) before the boiler chucks it, why did he not adjust the pressure to reasonable amount as specified on the facia.

The flow through the boiler should be just under 10l of water (this has no relevance to pressure indicated on the pressure guage). At this flowrate, boiler will deliver hot water @ cold water in plus 35 degrees. Extra heat generated will not kill the boiler. You have three stages of control. 1)control knob, 2) 85 degrees C and 3) 95 degrees that pops the pilot.

Burner should fall back to low burn to keep pace with setting on the HW control. It would then switch between the two burns to give tempered water as required/ set on HW control.

I am in Bearsden.

 

[McCombi]

Think i may have given advice on wrong boiler so removed post

 

[biscuit77]

Fan venturi

 

[DP]

Fan venturi

You cannot be serious

Should you be suggesting cures based on assumption

 

[biscuit77]

You cannot be serious!, way to go mcenroe, fan venturi ill put money on it

 

[raptor4109]

the internal pressure on the gauge was fine, over 1Bar. I think he adjusted the pressure on the cold feed in - the last pipe on the right from the front of the panel.

DP - the burner runs flat out then cuts out (pilot light remains on) no modulation that I can see. Flow rate through the tap is plentiful, certainly not a dribble as I'm straight off the mains here.

BG engineer coming out tomorrow between 8-1 so hopefully he'll dig a little deeper. I shall update when he's been.

DP - I may book some of your time if BG fail again

 

[DP]

You cannot be serious!, way to go mcenroe, fan venturi ill put money on it

Put you money where your mouth is. What are you willing to bet it is not the venturi?

Raptor, will bath tap running full belt, what is the temperature on the guage when water is good and hot on the tap? Clock the reading at the point the burner goes out.

I think he adjusted the pressure on the cold feed in - the last pipe on the right from the front of the panel.

To do this, he would have had the white case off. If he adjusted the hot water flow rate from front of the case, then that is a new one on me.