Problem with Potterton Netaheat Electronic boiler -- clicks madly and refuses to start

[Ian Chapman]

I'd appreciate any guidance on a problem that has just appeared on our Potterton Netaheat Electronic boiler. Sure enough, it showed up on a Friday evening in the winter (our local heating company only works on weekdays) while we have two small kids in the house over the weekend, so I'm keen to hear any suggestions.

We noticed during the day yesterday (Friday) that the boiler was clicking a few times when it started up. The flame in the boiler had lit okay, but it sounded as if the boiler was ignoring this and was repeatedly trying to re-ignite it.

Later in the evening, we heard a longer burst of loud clicking from the boiler and, when we went to investigate, noticed a burnt, sooty smell which seemed to be coming from the boiler. We switched off the power to the boiler immediately.

A couple of hours later, we felt brave enough to try switching the boiler back on. It started okay and heated up normally, with no clicking and no further burning smell. We left it on for a couple of hours while we kept an eye on it, and then we switched it off just before going to bed.

Today (Saturday), we have tried switching the boiler on several times, but each time it clicks rapidly a few times during its attempted startup and then seems to shut itself down completely. There is no sign of a flame inside the boiler at any stage.

Our situation isn't desperate -- we have portable heaters which will get us through until we can call in a professional. I'd like to know what to expect, though. Do these symptoms point to an obvious cause? If so, is it likely to be expensive to fix? Also, just in case the boiler refuses to misbehave once it's in front of an expert (not unheard of!), is there anything that we can do beforehand to provoke the problem?

Many thanks in advance for any suggestions. In return, I'll post again later to say how things unfold.

[raden]

In message , Ian Chapman writes

......

Sounds like it's not flame sensing

due to (In % probability) ...

pcb not working properly

or

HT lead is broken

or

bad earthing (due to e.g. corrosion)

or

electrode not in the pilot flame

There are two types of netaheat, one with a spark generator, and the other with a sequence board (407676)

[Ed Sirett]

The flame sensing on the earlier types is by pilot heating of a liquid expansion phial to turn the main gas on. Since they see no flame at all it must be an ignition problem.

[raden]

Ed, I think you're getting confused with the mercury vapour switch here.

Even the old spark box netaheats have electronic flame sensing. The bit that gives it away is the fact that it keeps on clicking (i.e. sparking), so it's not sensing the pilot flame.

[Ed Sirett]

I thought they stopped clicking because the flame shorted the HT. The OP is saying that he sees no flame but the pilot flame is tucked away at the back right of the main burner and may be difficult to see.

[raden]

"We noticed during the day yesterday (Friday) that the boiler was clicking a few times when it started up. The flame in the boiler had lit okay, but it sounded as if the boiler was ignoring this and was repeatedly trying to re-ignite it. "

This bit

"Today (Saturday), we have tried switching the boiler on several times, but each time it clicks rapidly a few times during its attempted startup and then seems to shut itself down completely."

is now confusing me, as neither version stops trying to ignite if unsuccessful, they just keep on sparking

[Ian Chapman]

Many thanks to Geoff and Ed for your thoughts so far.

To clarify: when we heard the clicking on Friday evening, the blue flame in the boiler was clearly visible through the little round window in the front. However, on Saturday, there was no flame visible through the window at any stage.

The problem has moved on a stage further now. When we apply power to the boiler, all that happens is that, after a few seconds of the normal sound (pump running?) we hear a single "thunk" sound and the boiler goes completely dead, as if an internal cut-off has tripped. There is no longer any clicking or any flame -- indeed there is no further sound.

It's possible that, on Saturday, I mistook the "thunk" for the start of the clicking that I heard on Friday -- perhaps in my haste to switch off the boiler at the first sign of trouble!

Many thanks again for your replies.

[Ian Chapman]

That was a good call! The problem was on the main control board. One of the visible components (a power resistor, I think) was blackened and another under the sealed plastic cover had clearly become very hot too, because the PCB under one end of it was charred and one of its legs had become completely de-soldered from the board. That presumably explains the burning smell and the gradual failure.

It is the latter -- 407676 is the number of the board which needed to be replaced. I'm waiting on the bill to find out how much we get charged for the new one, but at least it was a clear case of replace versus repair, as the damage to the original PCB was fairly serious.

I asked for a routine check of the boiler at the same time, and it's a good job that I did, because the earthing bracket associated with the spark generator was 80%+ eaten away. Hopefully by having that replaced now, we've saved ourselves the cost of another visit in a short time. Otherwise, the boiler appeared to be in good condition.

Many thanks again for your help.

[raden]

In message , Ian Chapman writes

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