more boiler problems!

[otherparty]

Hi all

Re Potterton Performa 24 combi

After getting the PHE cleaned a couple of months ago - it was full of limescale - the water is again not getting properly hot. Problem is as follows:
Turn on HW tap, boiler fires up and heats the water. Burner then goes off (as expected), but takes too long to come back on again. Result being water goes cold before being heated again. So hot-cold-hot etc. [Although when i say hot i really mean only warm!]

In the period when the burner is off the boiler makes a kind of ticking/whirring noise - it's as if it's trying to fire up but can't. I'm by no means an expert, but surely it can't be the PHE again? Could be diaphragm i guess - last time i changed it was about two years ago - but boiler has no problem firing up when tap is first switched on.

What do you guys think?

Cheers.

 

[dcawkwell]

Classic plate heat exchanger blocked.

Or diverter valve not diverting properly.

 

[otherparty]

pretty sure it's not DV - ch flow pipe stays cold.
And PHE was properly cleaned (by a pro) only two months ago!

 

[Agile]

Sounds like the plate is not transferring heat properly.

What did the "limescale" look like?

The boiler should modulate back instead of switching off.

Just because it was cleaned by "a pro" does not instill the view that it was necessarily done properly!

You may have another fault too.

Tony

 

[otherparty]

Sounds like the plate is not transferring heat properly.

What did the "limescale" look like?

The boiler should modulate back instead of switching off.

Just because it was cleaned by "a pro" does not instill the view that it was necessarily done properly!

You may have another fault too.

Tony

Tbh i didn't pay much attention to the appearance of the limescale. The guy first tried with a standard (industrial) limescale remover, which improved the situation, but the water didn't get fully hot. He then came back and used Power Flush FX2 instead, which seemed to clean it properly. Indeed, for about a month and a half, i had pretty hot water - even on max flow.

By 'modulating back' does that mean the burner should stay on (with a smaller flame)? Just to emphasize what i mentioned before, when the burner goes out, it sounds like it trys to come on again fairly quickly (re whirring/ticking noise), but only comes on after a few ticks (and after the burner indicator light comes on). Is that typical of a PHE problem?

 

[dcawkwell]

Yes plate heat exchanger classic symptoms

If you had limescale the problem would have been very poor flow.
If it isn't heating it bits of rust from you central heating blocking it
at the boiler side. If you have a dirty system it can block up again next day.

 

[otherparty]

i just found this post elsewhere:

The best solution for blocked plate heat exchangers is powerflushing the system, provided the boiler can withstand fx2.
Changing the hex, or only cleaning it, is fairly pointless as the reason it got blocked is crap in the system. If you don't clean the system, you have a high probability of reoccurance.
Powerflushing will clean the system and the hex.

Read more: //www.diynot.com/forums/viewtopic.php?t=55906#ixzz2K7Pqb22S

would you agree that a full flush may be what is needed?

 

[Agile]

Without a thermal survey of the boiler I cannot be sure of exactly what the problem is but it certainly sounds like the plate is not transferring heat.

Until the cause of the problem is known then a suitable solution cannot be found. You said limescale but that is less common hence my questions about it. Its more common for iron oxide debris to block the plate.

If the heat is not all being used then the boiler should proportionally modulate back but not go off.

The boiler should smoothly reignite within a couple of seconds. Sounds as if you may also have a slight problem there.

Tony Glazier

 

[otherparty]

Just noticed that the whirring/ticking is happening with the central heating system as well (when DHW not in use). The 'whirring' seems to be the fan kicking in, but then switching off when the burner doesn't ignite.

 

[otherparty]

The weirdest thing happened last night: the problem resolved itself ! The burner no longer cuts out and hence the water stays hot.

Am i right in thinking this may indicate a temporary blockage in the PHE (which has now washed itself out)?