central heating boiler problem --- sludge? Wrong advice?

[FerryBig]

Hi all

My 13 year old Potterton Envoy Flowsure Plus has developed a problem. It is covered by Domestic and General who contract Baxi Heating. The boiler is a condensing combi boiler with a 50L sealed hot water storage tank. The storage tank has a T and P relief valve on the top and a few weeks ago it started passing. This has happened once before years ago and the Potterton (Baxi) engineer replaced the valve and all was fine again.

So, I called D&G and an engineer came out. I told him the valve needed replacing on the hot water tank and he said it was "kettling". He then proceeded to replace the pump and showed me the old pump which had some sludge on it and told me that I needed a power flush.

I'm not completely ignorant and lacking of common sense but it occured to me that the valve passing has nothing to do with the pump but he disagreed and buggered off telling me it was sludge that was the problem. Once the boiler had heated the tank again, it started passing and a day later it was also passing when the sytem was completely cold which confirmed to me that the valve needed replaced as there couldn't be any over pressure in there when cold, right?

Next I contacted D&G again and they told me they couldn't send anyone out until I had got a power flush done (£300-£400) to remove sludge. I disputed the engineers diagnosis and they agreed it sounded wrong, so they sent the same guy back out who this time agreed and told me he couldn't get the part and buggered off.

I looked up this part on the net, contacted a few suppliers and they had the part in stock no problem. Relaying this info back to D&G they said Baxi can only use certain suppliers but if I could get the part fitted by a 3rd party plumber/enginner then fine, send the invoice and they will pay for it.

So, new part fitted and no problems for a few days other than needing to top up the water pressure even though I can't see a leak anywhere????.

This morning I was having a nice hot shower and heard the overflow ****ing water outside and to my suprise, the new valve is passing but only when hot.

Now I need some impartial and proper advice, does this system need a power flush to cure the problem or is there something else going on here? Should I get D&G back to this? They think it's sludge and are hesitant to come back until I've had this done.

PS the engineer said it would be fine for a few months after he fitted the new pump.

I pay D&G £20 a month and this is the first repair for 2 years, so that's £576 without a call out and naturally I'm keen not to get ripped off/fobbed off and spend another £300-£400 on a power flush.

BTW the boiler is also making a rattling noise since he replaced the pump and I found a screw lying on the floor under the boiler!!!

 

[doitall]

Reads like the blind leading the blind.

What does the system pressure rise too when the boiler is turned on.

Sounds like an expansion vessel problem to me. Which one is blowing the primary or secondary PRV

 

[FerryBig]

Just under 2 bar.

Also, there is no problem when it's just the central heating that's on, no noise at all that I would associate with kettling

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• FerryBig
• 13 Dec 2012
• 1

It is the valve on top of the sealed tank that is passing when hot.

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• FerryBig
• 13 Dec 2012
• 1

 

[doitall]

It is the valve on top of the sealed tank that is passing when hot.

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• FerryBig
• 13 Dec 2012
• 1

So the secondary expansion vessel want's looking at.

Incidentally it should be 6bar and not 7bar.

 

[FerryBig]

OK

So is this big red tank the primary or secondary?

There is another smaller one connected with pipes sitting down on the floor

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• FerryBig
• 13 Dec 2012
• 1

 

[FerryBig]

Sorry for stupidity, the red one in the boiler is the primary, the one external is the secondary.

I can't get a pic of the secondary because it's behind boxing in but here is a schematic of where it connects.

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• FerryBig
• 13 Dec 2012
• 1

So you reckon this is not about kettling and sludge but the secondary expansion vessel and should get fixed under warranty?

Also am I right in thinking that the valve needed replaced anyway as it was constantly passing when the system was cold and stopped when I turned off the mains water supply?

And also (my last bit of thinking), would I be right in saying that there is nothing wrong with the secondary expansion vessel, it just needs recharged with air or something?

Many many thanks

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• FerryBig
• 13 Dec 2012
• 1

 

[doitall]

The secondary vessel is for the unvented cylinder and I would have expected it to be white.

Follow the pipe in you pic on the right hand side.

And yes it's likely to be duff at that age, unless it's been change before.

Don't think you'll get it done under warranty, but it should be covered under the boiler

Just read the add ons.

The prv goes as the result of a fault. Is it the temperature/pressure relief valve thats blasting out hot water that blows. or phone Potty first.

You need to get someone that knows the boiler. there should be some Bax/potty guys on later.

 

[FerryBig]

OK thanks, yes it a little white one down on the floor. By duff do you mean it needs replaced or recharged? If replacement necessary and the part is NLA will one with the same specs do?

Thanks for the advice.

 

[doitall]

Any white vessel with the same spec will do.

You can try a re-charge first if you like, info should be on the can.

See my edit in the last post.

 

[FerryBig]

Going to try pumping this up today (secondary expansion vessel) Zilmet 564 H

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• FerryBig
• 15 Dec 2012
• 1

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• FerryBig
• 15 Dec 2012
• 1

To 3.5 bar as stated in the manual

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• FerryBig
• 13 Dec 2012
• 1

Does that seem reasonable?

 

[Agile]

I would have told you what was wrong just from your first posting!

Its amazing that the nupty sent by D&G had no idea of the problem.

But thats the kind of person who has to work for those firms!

Tony

 

[doitall]

Don't forget to take the system pressure down to zero first.

 

[FerryBig]

Not just D&G though, the guy was from Baxi Heating who are supposed to know about Potterton stuff.

 

[FerryBig]

Thanks Doitall, I'll turn off the mains water and open a tap then pump it up. I'll report back later.

 

[Agile]

Probably strictly you should not be working on it as its an unvented cylinder.

Also most foot pumps dont easily pump up to 3.5 Bar!