Potterton Performa 28i - problems

[tukky142]

Hi I have a few problems with this boiler.

1. The pressure is increasing over 3 bar and water is coming out of the PRV. I assume this is down the the expansion vessel not having enough pressure in it. The thing is I had the expansion vessel replaced about a year ago - do they loose their pressure regularly? I will re-charge with foot pump and see if that sorts it.

2. I have had one instance of the CH being on put the rads not getting warm. I checked the boiler and the HW light on the boiler was flashing but none of the taps were open. I opened and closed a tap and went back to check the boiler - the HW light had gone out and the CH had come on. Is this the symptoms of a sticking 3 way valve? If so do you have to replace the whole valve or just certain parts? How can I check that the valve is operating correctly? Would it be worth flushing the system with anything?

 

[croydoncorgi]

At risk of appearing sarcastic and lacking sympathy....
Have you looked for recent postings on topics such as 'combi high pressure'?

Have you left the 'filling loop' valve open? If so the high pressure is due to mains water entering the boiler until pressure inside it matches the mains pressure. A Bad Thing.

Otherwise, the only way that the pressure can rise that high is because the system has been re-filled to that pressure (also a Bad Thing) or the secondary heat exchanger is stuffed (a Worse Thing because it'll have to be replaced).

It's most unlikely that the diverter valve in a combi will stick. More likely the diaphragm that drives it has a hole in it. The symptom of this is that the boiler gets increasingly reluctant to switch on in HW mode until the hot tap is wide open. Eventually, even full flow at the tap will have no effect on the boiler. (There's a strong spring that pushes the diverter valve in the other direction)

Why did you think there might be a problem with the pre-charge of the expansion vessel? (I really want to know!) Before you touch it, read the FAQ carefully.

 

[lor]

hw flashing is the boiler preheating hw in its store
expansion vessels in these r v. poor. esp in larger properties


croydon ref div valve you haven't worked on many Isars as this was a common prob due to design fault in the material used

 

[croydoncorgi]

Early electric D/Vs were certainly a problem for Vaillant!
But water-pressure types are so over-powered it's usually very hard for them to stick open against the spring and sticking shut is usually identified as 'water pressure too low'!
To be honest, I didn't know about a specific Isar D/V problem.

 

[ChrisR]

pssst - this DV's electric, cc! No diaphram, Tucky, but a motorised head.

You need to read the bumph on this boiler. The tap symbol flashes when it's doing the preheat of the tap water store. It won't be doing CH then, HW store is a priority.

I know there can be faults on the way these sequence things. The Fault finding chart asks things like "Primary water diverted to DHW preheating circuit?", which isn't exactly obvious without thought and temperature probes.

 

[croydoncorgi]

Whoops again - looked at the Performa 28 manual not 28i.
Anyway - I THINK we're agreed that the pressure problem in this case is probably not DV-related.

 

[gazthepottertonengineer]

Definately not DV

Definately Expansion vessel

 

[ChrisR]

I THINK we're agreed that the pressure problem in this case is probably not DV-related.

er - there was no suggestion that it might be related...

 

[tukky142]

Thanks for replies guys I plan to check the pressure vessel this week and re-cahrge if necessary. I will do it when I drain the system to replace a rad. Sounds like I dont have a problem with the diverter valve then - I will keep an eye on it.