Saunier Duval boiler problem - 'boiling dry'?

[jaz66]

Hi guys,

Long time lurker, first time poster.

I have a manky old Sauiner Duval boiler (non combi) running an open system - old skool, inherited in old house. Has always worked OK (if seemingly inefficiently) but a problem that I've come back to yesterday leaves me scratching my head.

When told to turn on by the programmer, the boiler autoignites as normal and runs for maybe 25-30 seconds, then the noise it makes changes, almost as if you were boiling a kettle dry - then it cuts out (I guess a thermo protect) and takes 20 minutes before it will fire again. Clearly this isn't enough to heat a house or make hot water.

I've bled maybe 6 litres from the lowest point, bled all rads (no air) and checked the expansion tank but am now stumped. Would appreciate any ideas for what is making this happen.

Thanks a load.
Jaz

 

[Slugbabydotcom]

Sounds like a knackered pump.

 

[Agile]

The pump has seized up.

There is a "knob" facing the front which can be unscrewed and exposes a shaft which can sometimes be turned to free up the pump.

This boiler is overdue for replacement although its fairly efficient.

Very few engineers will work on this make!

Tony

 

[jaz66]

The pump has seized up.

There is a "knob" facing the front which can be unscrewed and exposes a shaft which can sometimes be turned to free up the pump.

This boiler is overdue for replacement although its fairly efficient.

Very few engineers will work on this make!

Tony

Cheers for the prompt response. Had isolated the pump as the next area of attention! You're quite right about engineers staying away - have found it a real struggle in the past (hence my 'keeping it going' efforts to date)!

Ta
Jaz

 

[jaz66]

Hmm.

Had a look at the pump last night and it had indeed seized. Some manual intervention caused it to run again which did the job for a couple of hours or so, but the problem has returned (boiler sounding like it's 'boiling dry') - only now I get a similar sound from the rads - a gurgling, pumping sound. As before, all rads have been bled, but now the pump does at least seem to be turning. I suspect it may be that the pump is on the way out, but at the moment it sounds like it's running, the housing is vibrating and turning the 3 position switch causes the pitch of the sound to change, so it sounds like for the moment at least the pump is running ok...

Any more thoughts? Help much appreciated!

Jaz

 

[Agile]

My thought is that you should replace the boiler.

The pumps are quite expensive and the make and age does not justify a new one.

I suppose that if you are very mean then you might be able to fit an external pump!

Tony

 

[jaz66]

My thought is that you should replace the boiler.

The pumps are quite expensive and the make and age does not justify a new one.

I suppose that if you are very mean then you might be able to fit an external pump!

Tony

Ah ha! This might help then...

The system only has an external pump, some french effort that escapes me now. The boiler is a Saunier Duval Xeon, apparently a current product (?!?!). The pump I'm guessing can just be replaced for 50 quid parts or maybe 150 fitted, so I reckon that's my best bet. Suspect it is the pump as it ran when given some gentle encouragement with the back end of some molegrips

Jaz

 

[JohnD]

if you bleed the highest radiator in the house, does water squirt out forcefully?

Do you notice black or other sediment when you drain water out, and, when you drain water, does the feed and expansion tank supply the same amount of fresh water? (it might be blocked)

If you have a sediment problem it will tend to wear and clog the pump, and cause other blockages and noise. It is possible to do a DIY partial clean at modest cost

If you see a lot of mud in the F&E I would bale it out and sponge it clean, extra sediment will not help the system.

I am just a householder but have had something comparable

 

[jaz66]

if you bleed the highest radiator in the house, does water squirt out forcefully?

Do you notice black or other sediment when you drain water out, and, when you drain water, does the feed and expansion tank supply the same amount of fresh water? (it might be blocked)

I am just a householder but have had something comparable

Water seems to come out forcefully from every bleeding radiator

When playing with the pump I did notice that when closing out the isolating valve the stuff that trickled through was filfthy - like 100,000 mile old engine oil.

And there's no such thing as 'just' a householder

 

[Agile]

I am sorry, I had assumed your boiler was a dreadful 620/623.

The Zeon is rarely seen but very similar to an Ideal Classic and is a very compact heat only boiler.

There is nothing much wrong with them and they are not much more than 7-8 years old.

Just replace the pump which should be any standard heating pump.

Tony

 

[JohnD]

good, so you haven't got a blockage.

You have a dirty system, though, and you can do a DIY clean fairly easily using Sentinel X400 for 4 weeks, then draining and rinsing and refilling with an inhibitor such as Sentinel X100. The chemicals will cost you £15 each. A DIY clean, before you have a blockage, will be much easier, effective and cheap than if you wait until a blockage occurs.

If you can do basic DIY plumbing you can fit a Magnaclean as well, I guarantee you will be amazed and delighted to see how much sediment it traps. It will cost you about £100 and is fitted on a vertical 22mm return pipe.

 

[jaz66]

Thanks for your suggestions and help so far.

An update - the (external) pump now seems to be running sweet and is pumping very hot water. However, the boiling dry ('kettling?') problem continues and the rads are not getting hot. They've all been bled to within an inch of their lives but nothing doing. Some get warm at best, but not enough to heat house.

On a possibly related note, tipped some Sentinel Sludge remover into the expansion tank and when up there had a poke round with a torch to find the tank absolutely minging. Seriously, I expected a Pike to swim out from it, it's full-on David Attenborough stuff. That *can't* be good right?!

So, 1) any idea what to try next with rads? and 2) how do I make the expansion tank less scary - drain it down and manually de-mingify it?

Cheers again for your valued assistance!

Jaz

 

[JohnD]

(2)

If you see a lot of mud in the F&E I would bale it out and sponge it clean, extra sediment will not help the system.

Chemicals in the F&E do not help, you have to draw them down into the circulating system by draining water out of the bottom.

Since you have now mixed the chemical into the mud you cannot draw one down without the other.

 

[jaz66]

Chemicals in the F&E do not help, you have to draw them down into the circulating system by draining water out of the bottom. Since you have now mixed the chemical into the mud you cannot draw one down without the other.

Cheers - missed that in the post above. Will degunge the tank and start again.

Jaz