Potterton performa 30he combi probs.

[Umpkin_2000]

Hi, thanks in advance for any advice that can be given.

I have the above combi boiler,
The problem im having is when the hot tap is on, or having a shower, after about 5 mins of it being boiling hot, the boiler seems to cut off the ignition, and the boiler cools and the shower goes cool, after about 10 seconds, it fires back up and water goes hot again, but does it again 2 mins later.
Its almost lile the boiler is getting over tempertaure even though the hot tap is on full.
Its only done this recently, but is gradually getting worse, can anyone point me in a few directions to check. I have had suggested the plate heat exchanger as a posibility.
Just wanted to gather some more opinions.

Cheers.

 

[ianmcd]

Let the CH cool down, then run a hot tap and feel the ch pipes coming out of the boiler to see if they are getting hot when only a demand for HW is made

 

[Umpkin_2000]

Thanks for the reply, ill double check it tonight, but im pretty sure the pipes dont get hot towards the rads.

But will check tonight.

Cheers.

 

[ianmcd]

Thanks for the reply, ill double check it tonight, but im pretty sure the pipes dont get hot towards the rads.

But will check tonight.

Cheers.

That will indicate if you have a diverter valve or possible plate heat exchanger problem

 

[CBW]

Possible issue with pressure differential valve/microswitch?

 

[Umpkin_2000]

Ok, so i have done what you suggested, when the hot water came on, the pipe out to the radiators stayed cold.

But i am noticing other little problems, that could all be linked to the same problem, i dont know. The pressure dropped to below 1 bar, i filled to just over 1 bar, but i have noticed ive had to do that a couple of times lately, cant see any evidence of a leak.
And also seems to need the hot tap turned on more to bring in the boiler, and the flow sensor diaphram has been replaced couple of weeks ago when i had a prob with the shower, so thats ruled out.

Cheers

 

[ianmcd]

Most common problem with your boiler with those symptoms is the Hydraulic venturi has broken up

 

[Umpkin_2000]

Ok, that sounds promising, i just had a quick Google on that, this seems quite an inexpensive part, bout £15

Is this as easy to change as it looks in the boiler manual?

Thanks again for the replies, its ver much appreciated.

 

[ianmcd]

yes very easy to change but make sure you cover the electronics when doing it, or you will get water into the pcb, and make sure you fish out all the broken parts of the old venturi

 

[Umpkin_2000]

Thats good, might be a silly question, do i need to turn off any water systems to change this, i only ask as the manual never mentioned it. I will deffo use rags over the pcb, great advice.

 

[DP]

Four lights below 6 red leds, one of them will light up for duration of hot water demand: the burner light will be on for duration of burner on time- when burner goes out, light will go out. Check that hw light stays on or if burner light is coming on and off.

Run bath tap full flow and check if burner is still dropping out.

Six red leds, what led lights when burner light drop out

Is heating temperamental. Are rest of hot w after taps behaving similarly?

Reading the symptoms, could be several causes

 

[Umpkin_2000]

Hi, the heating seems to work fine, no issues at all.
All taps do the same, the DHW light comes on and stays on, its the ignition light comes on, the temp lights go up to top, then the ignition light goes off, and the temp drops to about 60deg, then ignition light back on, the temp goes up, and that cycles over about 4 mins.

Cheers.

 

[DP]

I would be looking at circulation and temperature rise and heat transfer during hot water demand. I usually look for 70 degree or thereabouts when boiler is set up to the book settings and has been serviced and is operating correctly during hot water delivery.

Primary side appears to be spiking temperature wise. You need to find out the cause, I know what I would be doing, given you a hint and hopefully you will find a heating engineer who can advance the repair from there.

Had same last month (sorted), only boiler was Baxi 80e- same clone

BTW, you do not need a new boiler

 

[Umpkin_2000]

So taking from what you are hinting at, you would look to the main heat exchanger, not the plate heat exchanger?

Although ive had the diaphram done, i still feel sometimes it takes a lot of flow to get the DHW to come in, but that could just be me.

I was hoping to do the work on this myself as i feel quite competent, so long as i dont touch any of the gas stuff.

 

[Umpkin_2000]

Ok, so having reread your message and you said about the water temp, i realised both my dhw and ch, were both at the max, so i bought them down and whilst its still doing it, its seems to have made it not as bad.

But also have now noticed as i was stood next to the boiler for some time, that it seem to do random pops and bangs, and slight whistle, that also i read is a symptom of blocked primary heat exchanger.
I may change the hydraulic venturi anyway as i have that ordered, so may aswell fit it.
For that i could do with a few pointers at to what water taps i need to switch off to change that, and what i need to drain before i undo it.

Cheers for all the replies ive had.

Ta.