Kettle-like noise from water tank then boiler trips out...

[hsabbers]

Hello,

We've recently moved to a modern/new-build house (11 years old) that has CH driven by an Potterton Suprima 50 boiler, fitted when the house was built (so also 11 years old).

Since we moved in, we’ve had a few problems with the boiler tripping out to lockout mode after just a few minutes of firing. A bit of research suggested it was the cause of the original factory-fitted circuit board in the Suprima 50, which apparently has an exposed wiring loom that could be prone to condensation build-up. We paid for a Gas Safe engineer to come fit a replacement board, with the enclosed wiring loom – assuming that would fix the problem.

In fact, this does indeed seem to have fixed the *original* problem, as the boiler will now fire more or less continuously for as long as needed. Recently, though, a new problem seems to have arisen, leading to lockout. Basically, after about 15 minutes of firing (certainly not nearly enough to bring a full tank to boiling point) an alarming bubbling noise starts coming from the pipes running under the upstairs floorboards that I assume must run from the boiler to the hot-water tank. This builds to a crescendo that, literally, sounds like a large kettle boiling (coupled with some metallic clanking from the hot-water tank). The Suprima 50 then trips out, and the boiling sound and metallic clanking stop essentially immediately.

To reiterate, when this point is reached the boiler will only have been firing for 15 minutes and the water in the tank (or rather, from from the taps) is *not* boiling. Sometimes, the running water will be little more than warm. Before this problem arose, I would set the boiler to fire for, say, 45-60 minutes for a piping-hot tank of water.

If I reset the boiler right away, it’ll then fire again – perhaps for another 15 minutes – before the same happens. As an experiment last night, I switched on the CH at the same time as the HW and – though I need to repeat the experiment to be confident of the result – this seem to quieten the noise and the boiler continued firing past 15 minutes.

So… any ideas as to what might be happening here?

Thanks,

Harry.

 

[ChrisR]

The water in the pipes & boiler IS boiling. It's not the same water that comes from the taps.

Usual cause is a dud or slow or blocked pump, or a load of air collected somewhere to restrict the boiler water circulation.
Look for an air bleed point near the hot water cylinder.

 

[hsabbers]

The water in the pipes & boiler IS boiling. It's not the same water that comes from the taps.

Usual cause is a dud or slow or blocked pump, or a load of air collected somewhere to restrict the boiler water circulation.
Look for an air bleed point near the hot water cylinder.

Thanks muchly - what would this air-bleed point look like and is it safe for me to do it? I'm very happy to pay for a professional if not.

 

[ChrisR]

 

[hsabbers]

Love the diagram - thanks! I'll have a look for this valve later (not at home right now). I assume I just open it carefully, with the system shut down, and wait for water to appear? I'll assume, also, that it's safe for me to do this. If not, please shout at me.

Harry.

 

[ChrisR]

Yes, it'll need a screwdriver, or pair of pliers or small spanner or something.
It's extreeemely dangerous, in that you might hit your head on the shelf above...

 

[hsabbers]

It's extreeemely dangerous, in that you might hit your head on the shelf above...

That's my biggest fear - I may be buried alive under towels and bedding. I'll tread carefully.

 

[hsabbers]

Just bumping this topic as I’ve conducted a few more experiments and have more information.

Basically, the kettling noise followed by boiler lockout now happens very quickly after the boiler has fired – usually within around 5 minutes. A lot of the noise seems to be coming from the circulator pump – a Myson Compact CP53. Following the manufacturer’s instructions, I unscrewed the manual restart knob and applied sideways pressure until water appeared, to aid venting (so say the instructions). This didn’t seem to help, as water appeared immediately (so I assume no air) and the problem remained the same. I should point out that the Myson’s instructions suggest that this restart knob can be fully withdrawn:

“Before switching the pump on the manual restart Fig 7 should be unscrewed and
withdrawn to engage in the motor shaft. Check that the shaft rotates freely, and
that the knob can be seen rotating on initial start up of the circulator. Screw
manual restart back in.”

However, I’m a little reticent to try this – is it safe/sensible to do with water in the pipes?

Also, as part of my experiments I have discovered that if I have the CH on at the same time as the HW, so that the rads get hot, then the boiler will fire beyond 5 minutes (and we get hot water). In other words, by running both the CH and HW, the kettling noise seems no more and the boiler doesn’t lock out.

We have a Gas Safe boiler chap coming on Friday but I’m simply trying to troubleshoot/isolate the problem as much as possible before he visits – so any further thoughts on what might be causing this would be much appreciated.

Harry.

 

[mysteryman]

Give it a twiddle as the pump maker says - it sounds like a duff pump to me.

 

[Agile]

Is the pump on setting "2"?

There are many possible causes of your problem. The boiler seems to be overheating!

Try turning down the temp knob on the boiler first. Should be about 2/3 way up.

I suspect the problem is internal and the engineer may need to use some thermal conduction paste. He may not have that or even know what to do with it even if he did! I could tell him if he telephoned me.

If you can measure the temperatures of the boiler flow and return pipes that would be useful diagnostic information.

Tony Glazier

 

[hsabbers]

Is the pump on setting "2"?

There are many possible causes of your problem. The boiler seems to be overheating!

Try turning down the temp knob on the boiler first. Should be about 2/3 way up.

I suspect the problem is internal and the engineer may need to use some thermal conduction paste. He may not have that or even know what to do with it even if he did! I could tell him if he telephoned me.

If you can measure the temperatures of the boiler flow and return pipes that would be useful diagnostic information.

Tony Glazier

I have tried the pump on both settings 2 and 3 (it was on 3 originally) -- no obvious difference and the problem recurs. Also, last night, I was brave and unscrewed and withdrew the manual restart knob: I felt it engage with the motor and I could feel the impeller turning, with no obvious resistance. More to the point, I then switched on the HW and the restart knob span around fast and free, so the impeller is clearly turning.

To be honest, I'm not sure how I would figure out which ones are the boiler flow and return pipes.

I had previously turned the boiler's temperature knob down to very low and again, this did nothing to fix the overheating/kettling.

As ever, really appreciating all the input here. I'm just trying to make the engineer's job as easy as possible, come Friday.

 

[5544]

might be with checKing the thermostat thermister (sat in a dry pcket on the boiler pipe on LHS of boiler) potterton recommend changing these as well as the PCB once that fails. since the thermister also fails. i believe from memory that the resistance reading should be 2Mega ohms at room temp, this could be a reason.

 

[hsabbers]

Thought I'd just post the conclusion here, in case it helps anyone in the future...

The engineer turned up and very quickly diagnosed a failing CH circulation pump as the problem. Two or so hours of hacking copper pipes out (cos the old motor was stuck) and we have a new motor and this indeed seems to have fixed the problem. He fitted a Grundfos brand, which he said was better quality than the Myson it replaced.

Anyway, thanks for all your input here. And very glad we took out a cover plan a few months back -- I dread to think how much all the engineer's work and parts would've cost otherwise.

Harry.