Vokera linea 730 intermittant hot water

[pinkus]

Can some one shed some light on the following: Last March we had a new combi linea 730 installed. One month later we had no hot water although C/H worked fine. Vokera Engineer came out and after sometime took out the domestic Hot Water Heat Exchanger,and said that it had debris in it and the system had not be chemically flushed (it was done a couple of Months before).
He replaced the exchanger and the boiler then worked fine (We then had it chemically flushed again on Vokera insistence) Then last Month, we lost the hot water again but if you ran the water slow it did come out Hot. Out comes the same engineer and this time the motor control valve had worn out. and guess what it was because the boiler had not been chemically flushed the first time. He then takes out the Dom heat Exchanger again flushes it, takes it outside and bangs it on the concrete.puts it back in now says system is fine, 2 days later the boiler starts playing up and we start to loose the hot water again, if you run the hot and cold together the water becomes hot then goes cold then boiler fires up again. Out he comes again and does the same but this time flushes both DOM & C/H Still as bad. BY this time I pulling my hair out and want a replacement boiler. Vokera say no way, they are stating that the system was not flushed out and that the debris from the C/H had got into the Dom heat xchanger, is this possible?.The other get out is they are saying that my Mains Inlet Pessure is not at 20mb(varies from 17 to 19 mb). Can anybody please give me some advice?

 

[Gasman1015]

Do you mean that a chemical flushing agent was just added to to system, and was it flushed by normal draining or power flushed.

All manufacturers installation instruction state that gas boilers require 20mb working gas pressure, only allowed 1mb drop from gas meter to appliance, which would indicate undersized gas supply pipe. (standard get out clause. i.e not installed to spec)

 

[ChrisR]

they are stating that the system was not flushed out and that the debris from the C/H had got into the Dom heat xchanger, is this possible?.

Yes. Some boilers seem to be more sensitive than others.

The HW goes hot and then cold because the boiler can't get the energy out fast enough (via the domestic HW h/e) so it has to turn off.

There is a magnetic filter thingy on the market now which MAY stop bits of grot getting to your h/e. At nearly £100 + fitting that's less than a full proper power flush.

 

[Slugbabydotcom]

Get the working gas pressure cheked at the meter if the pressure is similar there you may be lucky enough to find that the supply to your house is poor and thats up to your supplier to sort out.
The pressure at your meter should be 21mb + or- 1mb [not sure whether or not this was changed to 2mb maybe someone else can clarify] and then you are allowed a 1mb drop through your system which means that you could only have 19mb [18mb] at your boiler.
The rule of thumb is that you should have no more than 1 meter of 15 mm pipe leading up to your boiler and from there back toward the meter it should be 22m and even bigger depending on the system load and distance from the meter.
There is a calculation which can be done which can over-rule this rule which your corgi installer can find in his handbook.

With regards to the system water; adding chemicals for flushing complies with BS5449 but it seems as though your system is really crudded up. So if you want to avoid future problems best get it powerflushed anyway. Normally powerflushing is overprescribed but I sense that it is justified here.Theres a firm called Kamco which can give you details of local plumbers equipped to do it for you.
If the chemical flush you had was a 'powerflush' it is possible that the existing crud in your plate heat exchanger wasn't flushed out properly and will need cleaning again.

 

[DP]

Modern boilers have narrow waterways. Gone are the days when hot water heat exchangers were chambers with internal coils. These HEs went a long way before they got choked.

System cleanse cannot be done in a day. A system drain and refill will not remove system debris nor will addition of chemicals, protracted run and water dump. Hooking a powerflusher to the system will remove a fair amount of muck but not all. Turbulence created by the powerflusher will lift and dump the debris but where there is no turbulence (like above the base rib or certain parts of the base rib), result is existence of deposits to later cause problem. Following a powerflush, remove the air vent plug and examine; black jelly like substance will indicate existence of muck.

Best to chemically clean following maker’s instructions, powerflush followed by water analysis to see presence of debris. This is followed by addition of inhibitors. No two systems will be the same so different approach for each installation.

 

[pinkus]

Thanks everyone
I ramballed on a bit yesterday so i would like to clarify a couple of points,
1:The Vokera engineer now says that the system has little or no debris in it.
Transco are comeing out today to check the pressure.What i would like to know is are vokera boilers usually troble free? Would banging the heat exchanger on to concrete affect its performance,

Once again thanks to you all for taking the time to answer what to m ost of you will be simple questions

 

[DP]

In my books the earlier Vokera build quaility was the best (like on Vaillant VCW 242/ 282 or T3). Sadly marketplace compition has resulted in relaxation of build quality.

Banging the HE on the concrete has loosen the debris for it to be flushed. HE is not leaking so you do not have to worry.

Vokera spares are far cheaper than most other boilers.

The problem you have encountered on the Vokera would have occured on any other modern boiler using a plate to plate heat exchanger.

 

[corgigazza]

try this for magnetic filter //www.diynot.com/forums/viewtopic.php?t=22859&highlight=

had similar problem on vaillant vcw 242 even after new dhw heat exchanger and powerflush it still blocked up.

 

[pinkus]

Hi Everyone
Transco came out yesterday gas pressure was low now fixed
Vokera engineer came out today Replaced 2 ntcs? took water sample still thinks this is problem. Then had to call him back out as boiler still not correct, he then changed main board and pds, said nothing else could be done until water sample comes back.

Thanks
pinkus

 

[pinkus]

Boiler is just the same water gets to 56 then cuts out,

 

[Slugbabydotcom]

Glad to see you got somewhere on the gas pressure front
You are in the hands of Vokera now so its a bit pointless us posting any more ideas about it
please keep posting and let us know the rest of the story

 

[pinkus]

Vokera new ASM called me on Friday told him boiler still the same, He then phoned again to say that he had been speaking to some other engineers and that Vokera will come out next week and will change the water pump.
He then again stated that he was concerned about the water sample that they took from the heating side of the system. Asked what was used and told him it was flushed with Sentinel x400, he then asked for how long ,told him over 1 month. Oh my goodness he replied that is far to long and will have caused more damage to the system. I said it can be left for over 1 MONTH, but your not a heating engineer was the reply.
I went onto Sentinel web site and found that it is recommended that for bad systems(as Vokera said mine was)to leave it in for a month.

This does not give me much confidence in their ASM or their product knowledge as Sentinal is recommended by them.

 

[ChrisR]

X400 has only just started to work in a month! Exaggeration maybe but it's pretty innocuous stuff, mostly flocculating agents which get the bits into suspension, by allaccounts.
SOunds a bit of desperation cominto play by changing everything in sight.

Don't know quite where your 56 is but it sounds too low wherever. Poking about inside with a contact thermometer reveals a lot.

As withthe others, very interested to hear what the outcome is.

 

[ollski]

water quality is the cover all get out clause, if you don't clean it the warranty is void....if you do clean it and inhibit it they will tell you it was the wrong cleaner / inhibitor and too much / too little and foaming etc.

 

[bripl]

ollski you may of worked for a manufacturer in the past,never one of our products installer error the number one get out clause