Vaillant EcoTec Plus 838 versus 938

[RichS]

A question for Nick here I think

 

I've been trawling through old posts as I remembered a certain model boiler being recommended. Turns out it was the EcoTec 938 (38kw).

Looking at Vaillants web site that is one hell of a chunk of boiler, 60kg and 600mm projection. I assume these specs come from the fact that it has the "reservoir" of stored hot water.

Would I be correct therefore in assuming that the 838 is basically the same boiler but considerably lighter/smaller because it lacks this facility.

And if so what are your thoughts on the 838???

 

Thanks for any enlightenment.

 

 

[Fallingditch]

10 hours ago, RichS said:

that is one hell of a chunk of boiler, 60kg and 600mm projection.

 

The Ecotec Plus 938 certainly is one hell of a chunk of boiler (and one hell of a chunk of price tag too, at around 1400 smackers). On the other hand, the theory is that it will provide rapid hot water from its reservoir for handwashing, and in addition has the capacity to run two simultaneous showers, which means that I will not need to make use of a storage cylinder or thermal store. There are no solar collectors on site so all hot water will be provided by gas (LP not Natural). Will report back on actual tests in about a month. Will estimate running costs in 2018.

 

(Do understand that this is not addressing the OP question - will let others talk about the 838).

Edited February 15, 2017 by Fallingditch
typo correction

[RichS]

Thanks for that Fallingditch

 

I have just been comparing the spec sheets for the 838 & 938. The only differences I can see are the obvious weight/dimension and the maximum electrical power consumption differs by 20w.

The flow rate is the same for both boilers.

 

So it looks to me that if you forego the "instant" hot water element you get a smaller boiler that should still run two showers simultaneously.

 

Can anyone see ant flaws in my thinking??

 

 

[Nickfromwales]

Dhw specs of the 838

 

and 938

 

For running 2 showers, the 938 is far better imo. Very much similar results to having a 200ltr UVC as the stored water blends in to reinforce DHW delivery from the plate heat exchanger. 

Benefit with the 938 Is also when the house is occupied throughout the day and lots of small amounts of DHW are being drawn off, washing hands after loo / swilling the odd dish etc, as there is no delay in getting the hot water to the outlet other than the pipe run. 

Both good machines, but if you want as near to UVC performance as you can get without having a cylinder, it's the 938 all the way. For a combi the DHW delivery is quite remarkable, but remember it's cold mains dependant so a crap cold mains = crap DHW, ( REGARDLESS of the boilers capability to provide it ). . 

 

[palestino]

On 15/02/2017 at 05:59, Fallingditch said:

The Ecotec Plus 938 certainly is one hell of a chunk of boiler (and one hell of a chunk of price tag too, at around 1400 smackers). On the other hand, the theory is that it will provide rapid hot water from its reservoir for handwashing, and in addition has the capacity to run two simultaneous showers, which means that I will not need to make use of a storage cylinder or thermal store. There are no solar collectors on site so all hot water will be provided by gas (LP not Natural). Will report back on actual tests in about a month. Will estimate running costs in 2018.

 

(Do understand that this is not addressing the OP question - will let others talk about the 838).

 

I know much time has passed but I'm considering Ecotec Plus 938 and was wondering what are your thoughts 2 years later. Did you end up posting a report? I'm curious:
1) do you think the built in storage is sufficient for running 2 showers at the same time?

2) would you recommend it overall for a 4 bed / 2 bath home?

I really want to loose the water cylinder and use the space for storage

 

Many thanks

 

[Fallingditch]

On 05/02/2019 at 08:33, palestino said:

 

I know much time has passed but I'm considering Ecotec Plus 938 and was wondering what are your thoughts 2 years later. Did you end up posting a report? I'm curious:
1) do you think the built in storage is sufficient for running 2 showers at the same time?

2) would you recommend it overall for a 4 bed / 2 bath home?

I really want to loose the water cylinder and use the space for storage

 

 

 

OK so two years on and I am 100% happy with boiler performance.

 

1. Even though its on LPG, it has enough energy to heat two simultaneous showers. In fact, it is probably the water pressure which is the limiting factor; I am running two Hansgrohe showers which run at around 8l per minute (=16l per minute); I have 5 bar pressure but my flow rate is only just adequate for two showers. (That's because I am pumping from a borehole to a pressurised tank, and my pump/borehole capacity is the limiting factor, I believe).

 

The built in storage is not really a factor - that's about 20l only I think, and its really there so when someone turns on a hot tap, hot water is readily available without boiler having to fire up etc.

 

2. Yes - but measure or estimate your flow rate to the bathrooms. If you believe you can get 16l per minute, the boiler will cope. If you can't get that, or your pressure is too low, you will need to put in a pressurised cylinder and associated plumbing (plenty of threads on this elsewhere). This is the critical factor!

 

3.Unexpected benefits: we have underfloor heating. The wunda mixing valve which I installed in not effective at controlling low temperatures. But I found out to my surprise that it is entirely acceptable to run the boiler at 43, or 40, or 35 (or even 30).  So that's what I use to control the UFH temperature depending on time of year. Really rough and ready, but not a big deal in the scheme of things. (What I need to do and I don't know whether it is possible is to remotely control boiler temperature, and set that according to weather forecasts ...).

NB this boiler temperature is independent of the DHW temperature, which is set to 65.   

 

4. Running Costs

We've now run this setup for two years with average three people in a very well insulated 200 sq m house.

 

- heating goes off (say) 1st April. comes on (say) 1st November. We use heating during that time for hot water and all gas cooking.  We buy two bottles of 47kg at a time (typical price £55 per bottle in NE Essex) and they last 6 months with no heating.  So I estimate we spend maybe £220.00 pa on hot water and cooking. (or four bottles - fag packet, I know).

 

- the house is well insulated, and has high solar gain.  Our biggest problem is overheating (so we open the doors and windows to control temperatures - even when the underfloor is on). Our total gas consumption during the last year was 12 bottles.  Take off those four bottles for washing & cooking and that leaves 8 bottles for heating or £440.00

 

Could I work this out more accurately? probably. But tbh, at these levels of consumption, I am not very concerned. (I have other issues!)