Vokera 20-80 RS Flowmatic hot water variates

[Yellow Peril]

At the moment the shower varies from hot to cold for a few minutes then the boiler kicks back in. I can manage a quick shower (I have no hair) before it goes cold. Also, some days just turning the shower on (there's good flow) isn't enough for the boiler to kick in and I have to click the constant switch just long enough to fire the boiler, then everything's ok. Sometime once a day is enough, but others if the hot water hasn't been run, I have to repeat the (prodding the sleeping bear) process.

I've cleaned the fan blades and the venturi which made things better, but this was at most three weeks ago and I find it difficult to believe that they would become fouled in such a short time.

I would appreciate suggestions please.

 

[DP]

A service would not go amiss

Is the spindle on the left ( under the pump) retracting to put fan to full speed ?
Is the fan running at slow speed when no demand on boiler?
Is the spindle on the diverter pushing out to operate the microswitches when hot water demanded?
When boiler does work, once temperature achieved, does the burner drop to low flame for hw as well as for ch.
is the fan running at full pelt when demand applied to boiler

Quite a few variable here, diaphragm being one of these

 

[Yellow Peril]

Thanks guys,

How long would you expect a diaphragm to last before requiring replacement? I lose track of time, but I have replaced both diaphragm and diverter valve within the last two or three years.

The fan does run at slow speed with no demand, the spindle does move out on demand. When the shower is running, it starts at full flame, runs for 2-3 minutes, drops to low flame (or none - quite hard for me to distinguish) and then kicks back to full flame after a shortish delay and this is when the water cools.

I have a couple of spare diverter valves after replacements, because I was led to believe that these were difficult to service. If that's not the case I could service one of those.

My boiler is well over 24 years old and over the last twenty years I have replaced virtually all of the significant parts of it.

 

[ianmcd]

Have you bled the DHW heat exchanger ? The valve is not difficult to service, does it only do this with the shower? or does it do it when you run a hot tap too ?

 

[DP]

Look again, quite likely the burner is going out instead of going to low flame
Compare HW demand to ch for visual of low flame. Low burner flame is almost nil flame.

I have never replaced any diverter valves, manifolds or other items other than service components like diaphragms, seals and glands. Every brass main component is serviced. Part changers throw parts at boiler to fix faults. Cracking boiler that responds well to proper service.

You said the pin comes out. That will be on the diverter.
What about the flow manifold, unit below the pump- does the pin pull in when there is no ignition?

Run a hot tap, stand in front of the boiler, look through the small aperture in the white cover. At full turn of the hot water control knob, the temperature on the gauge will be 70, you should have 9.5l of hot water at the tap. You can monitor the hot water by feeling the second pipe in from right. Reducing the setting on the control knob will result in a click and lowering of burner flame size

 

[Yellow Peril]

Thanks, Unfortunately the temperature gauge hasn't worked for some time but I will conduct the visual checks.

As it's a quite quick and cheap fix, is worth changing the diaphragm anyway?

Terry

 

[ianmcd]

Again does it only do it when running the shower or does it do it while running a hot tap

 

[Yellow Peril]

Ian,

I haven't left the hot tap running long enough to see if there's a temperature fluctuation, but I often have to fire the CH up long enough for the boiler to kick in, then switch it off and if I turn the hot tap, or shower on, the boiler will normally start up.

I also should have mentioned at the start, that I live in and extremely hard water area and we constantly suffer from limescale problems.

DP, I haven't ignored your suggestions and will certainly run through those checks that you suggested. I can monitor the water temperature quite easily as the boiler is on the wall in my kitchen a short distance from the sink.

Terry

 

[Yellow Peril]

OK Guys,

The pin on the flow manifold comes out when CH is switched on and goes in when off. It appears to stay in when HW is running. I cannot see a flame when main flame isn't running, but the pilot light flame appears to pulling slightly by the fan.

The problem does occur both with the hot tap and the shower.

When I altered the heat for the hot water the the flame cut out all together rather than being a gentle reduction. I had to twiddle to get the flame back again - possible faulty switch? It is one of the very few items that I haven't replaced over the years.

Terry

 

[Yellow Peril]

...and I have bled the heat exchanger and there was no air present.

 

[Yellow Peril]

I checked this morning while the shower was running and the pin on the flow mainfold remained out whether the water produced was hot or cold.

i don't know what the pump is set at (how would I tell?) but it hasn't been changed since it was fitted and the boiler was behaving itself.

At the moment, i need to fire the boiler up via the CH switch just prior to needing hot water for the shower or tap to get the boiler to fire up. Prior to this after the initial poking the sleeping bear the HW side would kick in virtually all day with out the CH having to be flicked on

Terry

 

[Yellow Peril]

I'm referring to the other micro switch under and to the right of the pump, which I'm guessing is the flow diaphragm.

 

[DP]

The manifold, shall we say under the pump, is the flow manifold.
If the spindle is not pulling in during hot water demand, then there is the problem

Try CH, pin should pull in.

Going by what you have posted, ch starts the boiler and hot water works if ch has been on.
No hot water if no ch.

Air in the system would do that


That pin/ spindle needs to pull in. Only then will fan go to high speed
If pin is pulled in at all, even when no demand exists, then you do not have slow fan run

Which is it.

 

[Yellow Peril]

OK guys , here's a catch up. I had the front off the boiler and decided as I wasn't going to have time to clean the venturi properly, I would have a bit of a scrape round (in situ) in the section where the plastic pipe connects. Glad I did because now, I'm getting a half reasonable shower. There is a slight variation in temperature, but it quickly returns to full heat. Also now, when the boiler isn't running full bore, although I can't see a flame, I can hear that something is still running and not just stopping between bursts. So I'm guessing this is all pointing to the venturi having a thorough clean being replaced. However I'm still having to flick the CH switch on and off to get the HW side to work. Is this likely to connected to the Venturi problem or is it something different all together?

Terry


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please see https://www.diynot.com/diy/threads/diy-gas.8090/
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