which gas combi boiler. Vaillant 838 or 938 boiler and why? efficiency?

[Z. RANA]

ok which boiler Vaillant 838 or Vaillant 938, is best or most suited for the following property with following needs

15 double sized radiators. maybe add 1 more in the future.

6 bedroom upstairs
one main bathroom
one ensuite

2 large living rooms down stairs.
2 kitchens
one wc. (maybe add a shower to this, although probably won't as it not really needed)

currently we have in both showers both the electric and combi option for shower. this is because if the electric shower breaks we can use the combi for showering. and if the boiler breaks we can use the electric shower etc.. both are a back up for each other.

I prefer to shower with the combi in the ensuite. the main one is mainly on electric shower...

the reason i ask this question is because our stop tap allows about 10 litres per min . 10L/M.
so the 838 and and 938 give a flow rate of 15.9 l /m however the 838 can only give out what it gets in. so if it only gets 10l/m from the stop tap, its flow rate will be that. i.e 10l/m.. therefore a waste of 5.9L/m .

however i called vaillant today and they said the 938 has two cylinder tanks in it which store water providing instant hot water where as the 838 has water on demand i.e it heats it up as you go along. therefore the 938 can give you a flow rate of 15.9l/m although it may only gets 10l/m. this is because it stores the hot water and uses this as you use the shower...

i hope I'm making sense.

the total kw of all the double radiators at t50 is about 23.5 kw and at t60 is 30kw. so 38kw boiler should work giving 100,000 btus and 30kw of energy.

when i shower in the ensuite the shower is great. however if someone in either kitchen opens the tap or even the wc or even in the bathroom. thats a potential of 4 taps diverting the flow of hot water from my shower. there is an obvious and drastic drop of hot water pressure, depending on how many taps are opened whilst i shower... the problem may only be for a few mins but its there..

if i am going to pay £2500-3000 for a new boiler fitted. i might has do some homework to ask which is the best boiler and which is most efficient etc...

so once again.

1) which is the best boiler on the above info..

2) and my main concern is the efficiency will the 938 cost me more to run over the course of eg 10 years... (as i will get 10 year guarantee with all the bits that i need to get this amount of cover) annual service.. etc..

average 10/20 showers per week on the combi boiler.

just two questions.

thanks

 

[simond]

You have neglected to say why you have settled on the above two options.

Both boilers will give a maximum of 10 litres a minute HW in the scenario you describe. The twin tanks of the 938 will add nothing, but more breakdowns if my experience of the 937 is anything to go by.

If you want to boost the HW supply you have to look at raising the water flow rate available.

PS: Did Vaillant tell you that they will take £94 off your card for every in-warranty callout until it can be proved that the cause is inside your boiler and not an external or installation defect? Vaillant are going to the dogs in the UK.

 

[Gasguru]

Sort the flowrate issue out first.....then decide on a boiler setup. Get the pressure measured both static and dynamic (ie. at various flowrates) to track down the problem. A 6 bed house deserves better than a combi. Give Vaillant a miss....long since lost their way and few gas installers rate the company anymore. Don't believe any of that German quality rubbish...they're churning out junk these days.

 

[Z. RANA]

not 100% sure why i opted for the above two options. i had mixed opinions and every time i called someone out they all gave different views.

1) the british gas guy said 832 will do the job. but he never looked at the house, the radiators, loft insulation. he asked me and i answered : 15 rads and 1 bathroom and 1 shower. he said 832 will do the job well.838 will also do the job, but extra pipe work will be needed. he didnt talk about how to increase the water supply via the stop tap. as he was the first guy to come around. i should have asked him this but forgot to ask this.

2) 2nd guy and first from worcester said 32cdi, 34cdi, 36cdi will all do the job. depending on my budget. he told me i need to buy the filter and the timer for the 10 year warrantee.

3) 2nd guy from worcester said said 34cdi he installed for a 14radiator system and it was touch and go. so i have 15 and they are all double so i should go for about 36cdi or even 38cdi.

4) forth guy came from vaillant and he said 38kw or 42kw would do, but the 42 would be expensive as its goes into the commercial range and so he suggested 40kw baxi. which was better priced.

so i have ranges from a confident 832 to a no way less then less than 36 to a confident 38-42kw. I'm in a twist.

i agree that it might have more breakdowns as, it has more parts and these more parts mean more possibility to break. also iv read on this site the 938 not as good. but if i get 10 year guarantee i won't be too bothered.

i didn't ask about the £96 per visit by vaillant, i dont like the sound of this..

 

[Z. RANA]

Sort the flowrate issue out first.....then decide on a boiler setup. Get the pressure measured both static and dynamic (ie. at various flowrates) to track down the problem. A 6 bed house deserves better than a combi. Give Vaillant a miss....long since lost their way and few gas installers rate the company anymore. Don't believe any of that German quality rubbish...they're churning out junk these days.[/QUOTE


how do i increase the flow rate?, the stop tap is open full. this is a vital point you made. and a crucial initial deciding factor. thanks!!1

 

[ajr183]

If your set on a combi either a Worcester 440 or 550 or Veissmann Vitodens 222-F.

If it was my place i'd be going for the Veissmann.

Expect to add another £1k at least.

 

[simond]

Regarding the size of the boiler for heating, if you can use this online ready reckoner you will be streets ahead of most of the people you have seen;

http://www.idhee.org.uk/calculator.html

Be aware that how many rads you have and what size they are is pretty immaterial; it is the size of the house and the insulation you have that are the deciding factors.

Once you have this info for your own satisfaction, keep calling people round until someone independently suggests the correct boiler size for heating. Then you will have your man.

Regarding the water for a combi, you don't have enough of it to work satisfactorily.

NB: I would normally say 4 quotes for what is a small domestic job with tiny margins is a chronic waste of tradesmens time, and will be reflected in their costs to everyone. Someone has to pay for multiple quotes, and it is you, the customer. However you seem to have got nothing sensible out of any of them - so on this occasion I will say their time is worth nothing.

Personally, if someone rings us and they've already got 3 quotes in the bag, I'm not going to come out and look for nothing. 25% aren't good enough odds to work for free; my quote will be chargeable, refunded if I get the job.

 

[Z. RANA]

If your set on a combi either a Worcester 440 or 550 or Viessmann Vitodens 222-F.

If it was my place i'd be going for the Viessmann.

Expect to add another £1k at least.

wow, not heard of viessman, they seem like a premium company.

98% efficiency is that true?

worcester are stating 89.9%
vaillant 92.5%

so 98% is a big jump?

 

[bernardgreen]

Do not forget that the rated effciency is when the boiler is able to work in condensing mode. If the temperature of the water returning to the boiler is above a certain temperature then it is not possible for the boiler to operate in condensing mode. The efficiency then drops significantly.

Many condensing boilers retro fitted to existing radiator systems are only condensing for a short time before the return water is too hot for them to continue condensing.

 

[ajr183]

wow, not heard of viessman, they seem like a premium company.

98% efficiency is that true?

worcester are stating 89.9%
vaillant 92.5%

so 98% is a big jump?

I my opinion the best on the market at the moment.

I would take any manufacturers efficiency claims with a pinch of salt. They're done under optimum conditions (VW) and unless you've got UFH then any condensing boiler will not get anywhere near the claimed efficiency.

 

[simond]

Have you fitted many Viessmanns, AJR?

 

[ajr183]

Have you fitted many Viessmanns, AJR?

I've fitted 2 of the floor standing combi's i posted above and probably 50+ of various wall mounted combi and system boilers.

They're are a step ahead at the moment IMO, the system boiler if fitted with their cylinder you don't need a zone valve to be fitted, their design and forward thinking are excellant, though i personally think they do promote weather compensation to much but that's my opinion.

 

[simond]

We've had mixed results but most of our domestic installs date back a couple of years or more. I liked the WB1B open vent a lot but we had problems with some 200 series, they were the 4 pipe systems too. The Lambda sensor was causing high Co on a couple. Havent tried the floor standing 2 series yet, sounds good.

Doing a quote for a 130Kw Vitocrossal at the moment, their commercial stuff is well made.

PS: Couldn't agree more about the weather comp

 

[ajr183]

We've had mixed results but most of our domestic installs date back a couple of years or more. I liked the WB1B open vent a lot but we had problems with some 200 series, they were the 4 pipe systems too. The Lambda sensor was causing high Co on a couple. Havent tried the floor standing 2 series yet, sounds good.

Doing a quote for a 130Kw Vitocrossal at the moment, their commercial stuff is well made.

PS: Couldn't agree more about the weather comp

Can't say i've had any issues to date again probably going back 3yrs.

I totally agree with what you said further up the thread re Vaillant, my partner and i were asked to do a boiler change in a block of flats, they were taking out some old Hammworthys and putting in 8x100kw Ecotec's in a cascade, we did our best to try and change their minds and fit 100kw 200w's but they weren't having it, 3yrs on i reckon there's 6 or 7 working at any given time. Vaillant's quality has drastically nose dived over the past decade.

 

[Z. RANA]

Can't say i've had any issues to date again probably going back 3yrs.

I totally agree with what you said further up the thread re Vaillant, my partner and i were asked to do a boiler change in a block of flats, they were taking out some old Hammworthys and putting in 8x100kw Ecotec's in a cascade, we did our best to try and change their minds and fit 100kw 200w's but they weren't having it, 3yrs on i reckon there's 6 or 7 working at any given time. Vaillant's quality has drastically nose dived over the past decade.

When I asked the Worcester guys they said worcester was the best. won the 'Which' award. The same with the Vaillant guy who said Vaillant was the best. Again won the 'Which' award. they both can NOT be the current winner... although the Vaillant guy did say he fits Worcester and other brands...

I was led to believe worcester were the market leader in recent times, and recently Vaillant have caught up and now over taken as the new number 1.. as Vaillant use metal internal components where as the Worcester only use plastic internals. and that Worcester were doing their best to catch up Vaillant however Vaillant were still the current no 1 , according to the Which magazine...

Now, until today, I thought Worcester and Vaillant were no 1 and 2 in any order. I couldn't care less which order as i was choosing between the best two. There were lots of other brands so if I choose either no 1 or 2 not knowing which is the best it would not make any difference, as especially if was to get 10 year warranty from the installation.

Now Iv come across a new brand which seems to as good or even better.. ????? Confused.