New boiler, new woes

[OVS]

Hope someone can offer me some advice on my problems with my new boiler. After 13 years of good service, my Vaillant Combi boiler broke down.

Recently (about 2 weeks ago), I replaced the boiler with a new Vaillant Combi (828 turboMax). Since using the new boiler, the shower water doesn't reach the hot temperatures it once did with the old boiler. Its maximum temperature is hot side of tepid, but not searingly hot the way I like it! The ground level water reaches high temperatures fine. By the way, what's the average expected temperature for hot water using a modern boiler?

The Vaillant guy came round today and after 1 minute of oooh-ing and ahh-ing, said that I need to power flush the whole system and only then will they replace the heat transfer unit inside the boiler.

I've just now got off the phone to my plumber and was shocked to find that a Power Flush would cost me up to £800!!!

Its far to much money for me to spend, but if its 100% the route of the problem I guess I'll spend the money. My main concern is that the reasons I was given for a power flush does not make sense. My old boiler heated up the water fine. If there is grime in the system I would expect the new boiler to work less and less efficiently over a period of time, say six months. The new boiler failed to send hot enough water up to my shower from the moment it was installed.

I wish I had brought these questions up when the Vaillant guy was here, but a 'power flush' didn't sound like a big job. I shouldn't have been so naive, ANY job is a big job for a @?%$£"^ plumber.

Any advice? Is a power flush my only option?

Thanks

[free.uk.diy.home]

Vaillant

Manufacturers require all replacement boilers are fitted to a system which has been powerflushed or chemically cleansed. If that job is not done, then its easy for them to void the warranty in the same way that the benchmark book must be signed off by a Corgi who did the installation/commissioning.

I think that will find that unless you have a powerflushing or cleaning done, then Vaillant can claim to void the warranty. I don't know if they would allow a DIY powerflush/clean acceptable in this regard. Martyn

[Lee]

Obvious question, did your previous model throttle the mains water flow through it and have you done the same for this one? This model will probably allow a higher flow rate than your previous boiler, which is going to equate to a lower temperature rise...

Our 828 easily heats the DHW to 70C, but we have the flow rate throttled back to around 9 lpm. (due to a problem we have with flow noise in the mains water pipes).

Lee

[John Rumm]

Don't understand that bit about the ground water temperature...

Do you mean the hot water temperature from taps other than the shower is OK?

Typically they have a thermostat that will limit the maximum temperature to between 40 and 65 degrees depending on where you set it.

There may well be an argument for flushing the system. However that is unlikly to be the cause of your current problem.

Well it won't make sense, when using a combi for HW it will be circulating the water heated by the burner through an internal loop, not your heating system.

"grime" in the system may reduce efficency of the heating, and may cause premature wear and corrosian in the boiler. It should not make any difference to HW performance.

Obvious thing to check, is there a water temperature selection on the boiler? If so is it at a maximum setting or can you turn it up?

What is the temperature from the nearest hot tap to the boiler like? Much hotter than the shower? (if yes then that would point to an issue with the shower and not the boiler)

Is your shower a thermostatic or pressure balanced one?

Is your shower one of those that required lots of water (i.e. big drencher head or extra body jets etc)? What happens if you turn the flow rate down a bit in the shower, does it get hotter then?

[Lee]

Ignore my other post, was looking at the flow temp on the boiler Doh!...

Looking at the specs, the 828 is setup to a temperature rise of 42C @ a flow rate of 9.5 lpm. If the incoming mains cold is say 10C, then that's only going to give you a DHW of 52C and that's if you throttle the flow the 9.5 lpm...

Lee

[andrewpreece]

I have an 828 and with the temperature control turned right down it gave hot water at 49C from ground water at 16C: that's a rise of 33C, admittedly at an unknown flowrate ( I cracked open a cloakroom basin tap to full throttle ). Now, I found it very difficult to keep my hand in water at 49C, so 52C would be unbearable. Also, the 828, as I implied, can deliver HW at different temperature rises, and I've seen 11 ltrs/min at a delta T of 35C quoted. I have also meaured the maximum temperature of HW with the temperature knob set to max. (fully CW), and that was 64C.

To summarise, I think that with a small basin tap cracked fully open, the maximum temperature you can get from an 828 is ~64C, and the minimum would be about the groundwater temperature plus 33C. This may help in determining if you have a real problem.

The engineer chappy seems to be suggesting that your HW heat exchanger is not working properly beacause it is gummed up with sludge from your CH system. I suppose that is possible, since the boiler loop has the CH fluid as its working fluid. I can't comment on this £800 for a power flush ( seems ridiculous though ), but I'd want to know if that was the problem first, so you need to find out, somehow, whether your boiler loop/DHW heatexchanger ( the sardine tin ) is gummed up with clag. That would be my approach.

Andy.

Andy.

[OVS]

Sorry, by ground I meant the downstairs tap, nearest to the boiler and yes its all fine other than the water from the shower which is situated one floor up.

There is a water Temperature selector on the boiler, and its already turned all the way to maximmum.

Its just the shower which is having this problem. Its a very basic shower unit. Only two knobs, amount of water and hot/cold mixture. You're right, the problem does point to the shower, but it worked fine with the previous boiler. With the previuos boiler I would set the mixture to 75%hot and 25% cold, now 100% hot water doesn't feel hot enough.

I've just tried this now, it doesn't make a noticable difference in temp if i decrease the flow.

I've decided to leave it as it is for now, the temperatures bearable for now and the central heating and everything else works fine.

I'm stumped, although saying that, it doesn't take much to stump me when it comes to anything to do with electrical stuff or plumbing.

Thanks for the reply John, and also to the others who have replied.

[Ed Sirett]

Others have said good things. The primary side should have been cleaned out before fitting anyway. Even BG only want about £500 for power cleaning so £800 is way way over the odds.

Since it is new we can rule out 2ndary scaling (and you might be a soft water area anyhow).

To get hotter HW from a T/max 828 you will need to do either or both of two things.

Firstly the there is a separate _MAXIMUM_ HW temperature control the top end of this is likely around the equivalent of 65-70C which is rather more than 'searing' more like 'flesh consuming'. However since the temperature of the ground floor outlets is OK this does not need moving. I.e. the boiler's maximum is not too low (otherwise you would not get hot enough HW on the ground floor).

Secondly you may find that you need to restrict the flow of water through the boiler in order to get hotter HW. This you can do on any tap by simply opening it less. However it may well be more convenient to simply restrict the water flow in general: for this there is restrictor it is underneath the boiler in the same fitting as the cold water inlet valve. The restrictor has a hex (about 8mm AF?) headed spindle, these are generally set to full open 'out of the box'.

If the 'plumber' who fitted the boiler did not sign the book saying what was used to flush the system then I would get him back to do so. [On pain of a complaint to CORGI if needed. Those of us who do thing properly are getting pissed off by the slap-dash who charge the same for doing less.]

[IMM]

When fitting a new boiler on an old system a strainer must always be fitted on the return to the boiler to catch any debris or sludge.

[Markus Splenius]

A suitable part is?

M.

[IMM]

A 22mm or 28mm strainer, available from

or any plumbers merchant.

[Paul Barker]

Look original poster, you need to establish the flow rate from a tap i the bathroom is as per the spec of the boiler. You won't have a wei guage so you'll have to get a thermometer, run tap and adjust until th temp is the cold tap temp plus the rise used by vaillant. measure th quantity of water passed in 20 seconds and multiply by three.

If this test shows that the boiler is functioning correctly you shoul take the the hot connection off the shower and see if there is a strainer. Is i blocked? Or if there isn't one to what extent you can clean the shower Is there a flow restrictor in the hot inlet? Try removing it.

You can buy a small powerflush machine (Rothenberger) for £300 plu vat. Buy your own rather than spend what you've been asked. I charg £350, but my area isn't the most expensive in the country.

Anyhow it is very likely a bit of flux or something has got itself u there into the shower.

Pau

-- Paul Barker

[Colin Wilson]

The flow rate may not be as high on this boiler so if you have a flow restricter in the cold supply to the shower, you may need to reduce the flow a little.

Just a guess though, i`m crap at DIY :-}

[Ed Sirett]

I have no problem with fitting one, however Vaillant _do_ specifiy two flush outs and _don't_ specify the use of a return pipe strainer.

[IMM]

Some makers do. It is common sense to fit one in an old system as it catches any crap before it get into the boiler. If using 22mm pipe best to use a 28mm strainer and have full bore isolation valves either side, for ease of cleaning with a drain down. In fact they should be built inside boilers. Alpha boilers have a cyclone system which directs crap into a trap.