Potterton Gold HE - Water goes cold after a few seconds

[Mindzai]

Hi

I have a Potterton Gold HE combi boiler. It has recently started to have a problem where the hot water will go cold after a few seconds of running. Some info which may be relevant:

• This happened suddenly, not gradually. One minute it was working, the next it was not.
• The fans/pumps or whatever makes the whooshing and whirring sounds in the boiler is still working while the hot tap is on (even after the water goes cold).
• The light on the boiler to indicate the water heating is active is on (even after the water goes cold).
• The digital display on the front of the boiler (which I assume shows temp) goes up to into the 90s just before the flame turns off. It then drops to 80 and the flame kicks back in. This cycle repeats, but the water never gets warm (though it is not ice cold like from the cold tap).
• The flow rate with the hot tap fully open is about 5.5 l/m.
• I have a closed central heating system (I think - there is no tank anywhere anyway).
• As far as I can tell the central heating is working - the radiator heats up.

Any ideas what might be the cause of this?

 

[bengasman]

Could be:

Lack of pressure.
Corrosion causing plate hex to block
Inlet filter blocked.

 

[Mindzai]

Thanks for the reply.

Pressure seems fine, the gauge on the boiler reads about 1.5. - though the flow rate seems a bit low to me, the boiler manual indicates it should be closer to 10.
Would the other two issues not affect the central heating too? Or does that have a separate set of components inside the boiler?

 

[bengasman]

Heating is a separate, sealed system; it has no external flow.

 

[Mindzai]

OK thanks.

I just isolated the boiler from mains and gas, drained it and checked the filter - it was totally clear of blockage.

I turned the boiler back on after re-pressurising it to 1.5 bar and checked the hot water - it didn't go cold this time though it did fluctuate from very hot to quite hot and back.

However it was making a lot of grumbling and banging noises so I turned it off again. Could it be that there is some air in the system or is the banging likely to be from something else? I'm assuming it's not air as I'd have thought it would just come out the tap?

I forgot to say, the boiler and central heating system is only a couple of years old, though I suppose that is long enough for corrosion to take effect.

 

[kevplumb]

though the flow rate seems a bit low to me, the boiler manual indicates it should be closer to 10.

what comes out depends on whats going in

However it was making a lot of grumbling and banging noises so I turned it off again. Could it be that there is some air in the system or is the banging likely to be from something else? I'm assuming it's not air as I'd have thought it would just come out the tap?

could be air in the system

nothing to do with the taps two seperate animals

 

[Mindzai]

OK thanks.

How would I go about getting rid of the air?

Re the pressure, the mains cold water seems pretty high pressure judging by how it comes out of the taps, it exceeds 10 l/m easily.

 

[bengasman]

Could be:

Inlet filter blocked.

 

[kevplumb]

water inlet filter ben

is there one on the heating

 

[Mindzai]

The cold water inlet filter is the one I took out and checked - like I say totally clear. The only other filter mentioned in the manual is "Flow Sensor with Filter & Regulator" which I haven't checked. Should I have a go at getting this one out too?

Incidentally I ran the heating and hot tap for a bit and the banging noise has stopped now. I'm still having the issue where the hot tap goes from properly hot to warm and back in a cycle though. This is better than cold, but still not ideal!

 

[bengasman]

water inlet filter ben

Is the only inlet filter is it not?

is there one on the heating

Wouldn't think so.

 

[bengasman]

Are you sure you checked the right filter? You don't need to drain the boiler to check the inlet filter.

Is the boiler only a couple of years old, or the pipes and rads too

Could be an isolation valve or stopcock in the cold to the boiler partially closed.

 

[Mindzai]

Are you sure you checked the right filter? You don't need to drain the boiler to check the inlet filter.

Underneath the boiler I've got 4 main pipes that go up into the boiler. The two on the right have a loop of flexible pipe (like a flexible tap connector) going between them. These two pipes each have a stop valve and I closed both of them. Then I disconnected the loop from the far right pipe. After that I had to undo another larger nut and sitting behind that nut was the filter (looked like a cylinder of wire mesh).

When I loosened the flexible hose connector from the far right pipe, water started leaking out smelling of the radiator inhibitor stuff. I did drain it for a bit to see if it was just water in the pipe but it kept coming so I tightened it back up and drained the system. After that when I loosened it again only a dribble of water came out allowing me to properly disconnect it and get at the filter.

As far as I could tell from the manual this is the only filter aside from the "Flow Sensor with Filter & Regulator" which I haven't touched. On the other pipes going up into the boiler, none of them have this removable nut that the filter was behind.

Is the boiler only a couple of years old, or the pipes and rads too

The whole lot was put in at the same time. Before that I had an old boiler with air vent type heating and a water tank. This was all taken out and replaced with the new boiler and radiators.

Could be an isolation valve or stopcock in the cold to the boiler partially closed.

Not sure about the stopcock, I'll to look in the manual as I don't know where that is. All of the isolation valves I could see were underneath the boiler, and they all appeared to be fully open aside from one, which was on this flexible loop. Opening that is how I refilled the system.

Thanks for the advice so far, really appreciate it.

 

[bengasman]

Maybe you can post some pictures.
One thing is odd, you mentioned 4 pipes, I expect 5 on a combi.
The stopcock I mentioned is not part or the boiler, sometimes people put them in so they can isolate the boiler from the water mains.
Do I understand it correctly that your system still uses the old pipes from the previous boiler? If they have not been cleaned properly, you could have debris ending up in the new boiler.
It also sounds like your filling loop is failing; that would be unusually early.

 

[Agile]

Just above and behind the pump is the auto air vent.

Is the air cap on the top just loose?

I would still suspect a blocked plate heat exchanger.

To confirm that I would do a thermal survey on the boiler.

Just by chance I went to one this morning but that was part of a solar installation.

Tony