Pump over-run = boiling up

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Pump over-run = boiling up

Post  Phil_J on Mon Jan 08, 2018 5:55 am

I have a rather old Boilermate III 140 circa 1999 in my house attached to a Potterton 50 boiler. Recently I had to change the GT-151 SAC PCB as some components were burnt out. Since doing this the boiler boils over on shutdown and shoots noisily up to the header tank on the boilermate. I can see that the demand to the boiler is stopped and that the main circulation pump over-runs for several minutes after the boiler has stopped. However, when the circulation pump eventually stops there is still sufficient heat in the boiler to boil the water up.

Is there a way to extend the pump running time?

I have calibrated/commissioned the card as per instructions but cannot seem to stop it boiling over.

Many thanks in advance for you help

Phil_J

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Re: Pump over-run = boiling up

Post  mike on Thu Jan 11, 2018 12:52 pm

Check for sludge etc

Mike
MGC/H2O
Norfolk

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Re: Pump over-run = boiling up

Post  Phil_J on Thu Jan 11, 2018 1:09 pm

Hi Mike

Thanks for the reply. I don't think it is sludge. I have drained and refilled the system a couple of times in the past month as the boiler was kettling and it hadn't been done for years., adding Sentinel x400 and leaving it a week each time. I also changed the main re-circulation pump at the same time. It's now on x100 inhibitor and x200 noise reducer. Although with all all the boiling up issues, the scale must have built up again quickly in the boiler as it is running noisy again.

I'm currently leaving the heating on permanently (not timed) and using the room thermostat to stop the boiler being on continually. This seems to keep the pump running regardless of the heating demand from the stat.

I seem to solve one problem and then a few days later something else plays up.

Thanks

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Re: Pump over-run = boiling up

Post  mike on Sat Jan 13, 2018 12:32 pm

You said water shoots up the header tank.

An easy route

Hence my sludge suggestion

Mike

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Re: Pump over-run = boiling up

Post  Phil_J on Tue Jan 16, 2018 5:55 am

Hi Mike

I have been mulling this over and am not sure if your last reply was to defend your first suggestion of sludge or whether you are sticking with it even though i say the system was flushed a few times.

The boiling up scenario only started once I had changed the GT-151 card which is why i thought it was timing or temp control related.

Should I look for sludge somewhere that didn't get flushed (Any suggestions of where?)

Many thanks again

Phil

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Re: Pump over-run = boiling up

Post  mike on Wed Jan 17, 2018 12:58 pm

Lets recap.
With heating off
And the boiler heating the store only.
When up to temperature and the BM III is satisfied. The boiler stops, The boiler pump still runs to take away any further heat.

New board fitted
Has both lots of jumpers in their places etc?
Boiler pump is new? New head or complete pump. If head only did you check old pump body for building inside?

Cleaner although good does not clean it all out.
It has years of build up in there. So will take time to remove.

When the boiler has stopped and the pump is on over run that heat has to go some where.
If it is going up the vent on the unit to the F & E tank then that is an easy escape route. Meaning it should but can not go where it should.
Have you checked the auto bypass valve?

Mike

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Re: Pump over-run = boiling up

Post  Phil_J on Thu Jan 18, 2018 1:01 pm

"With heating off
And the boiler heating the store only.
When up to temperature and the BM III is satisfied. The boiler stops, The boiler pump still runs to take away any further heat." - yes, but as soon as the over-run stops, the now non-circulating water boils in the boiler, expands and shoots up the return pipe to the store - it is plumbed so that there is an "external overflow" easy escape path to the F&E tank. I guess this T's off the return from boiler to store somewhere but the connection is under the floor and I haven't seen it.

New SAC board fitted and the same 3 jumpers put back in the same places.

It was a complete pump unit.

I think the bypass is working ok (how to tell?) but the problem happens when the heating is off, so the 3-way should have already closed the heating loop and opened the shortest circuit.

Thanks again for your thoughts.

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Re: Pump over-run = boiling up

Post  mike on Thu Jan 18, 2018 1:16 pm

You done the 3 jumpers
What about the 2 horizontal one over on the right?

Try turning the boiler pump down to 1.
If a new pump is it the new Grundfos one? As in the 15 / 50 /60?
If so they are very powerful.

With ref to the 3 way valve you are assuming all is correct.
Check the bypass setting and alter it to a point where it is really open.
See if it stops / changes anything

With ref to the vent, yes that is the easy route. So anything blocked or partiality block would / could create enough resistance for the easy route to be used.

Another thing to try is turning the boiler down a bit to a point where it may stop.

When you work out what it is it will be easy!

The 3 way may be faulty inside. The rubber balls on Honeywell valves can give trouble.
You could try removing the head and ensuring valve is open and try that if possible.

Also check the level in the F & E tank. Lower that as much as possible and that might stop the pumping over.

Is it boiling over?
Or just pumping over

Try the above and keep trying in the end you will get there.

Mike

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Re: Pump over-run = boiling up

Post  Phil_J on Mon Jan 22, 2018 4:36 pm

Sorry for late update - for some reason the pump keeps running now, even when heating is off and no demand on the boiler. I'm not sure why but at least it is quiet again.

It was boiling definitely boiling over before. - Boiler would go off, pump would over-run for about 5 minutes and as soon as the pump (yes it's a Grundfos 15-50/60) stopped it would start to kettle and then get louder until it explosively shot up the pipe into the header. (no pumps were running at this point)

I'll keep you posted of any developments, thanks again.

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Re: Pump over-run = boiling up

Post  mike on Mon Jan 22, 2018 4:56 pm

Well when the unit is satisfied ? happy and up to temperature (check that it is)
Then it will tell the boiler to stop.
Delay timer will run to get rid of heat from boiler.

But the pump is still running.
Is the store still asking the boiler for heat thus not satisfied? (check is supply to boiler / switched live)

If so the problem would be;

Boiler and or flow & return pipe from boiler to unit and back.
It may be that the boiler heat exchanger is badly scaled or blocked.

Check the above
And a thermometer would be useful to check store temperature
And temp from boiler on flow at boiler and at unit.
Also return temp again where it leaves unit and at boiler

Mike

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