Vaillant weather compensation - unvented system installation

[joncox]

I've seen Vaillant weather compensation discussed recently but want further opinions.

As a precursor to a loft conversion in an unextended 2 bed Victorian terrace, I intend to replace my S plan vented system (Potterton Profile 50e feeding 7 rads via microbore and 22mm gas supply throughout run; no TRVs) with a unvented cylinder and system boiler.

It will remain a one-bath property but I don't fancy a combi.

The mains is supplied by a 1in lead pipe which delivers a measured 27l/m off peak and c. 22 peak to kitchen and bath cold taps. I've not had the pressure measured.

I'm almost sold on having a Vaillant 618 and 155l Unistor connected via the VR65 control centre, but am dithering over replacing my Honeywell CM927 room stat (in hall) with a Vaillant VRC430 weather compensation unit. We do have an appropriate N facing external wall for the sensor.

Questions:

1) Should I insist on a pressure test (X bars..) from installer even though the flow rates seem adequate?

2) Would a very disruptive upgrading of the 1in lead supply pipe to 25mm plastic offer any improvement in flow rate (I doubt it..)?

3) What are the pros/cons of having the VRC430 weather comp. plugged into the boiler fascia - where it doesn't monitor room temp - or having it wall mounted in the hall, where it would monitor room temp?

The new boiler would be in the kitchen, which faces SW and gets lots of sun.

Thoughts from Vaillant installers (gas4you, simond..) very gratefully received.

cheers

 

[simond]

Is your house uniformly and well insulated? If not, WC won't be as effective.

The water flow seems good and is above average. Wouldn't do in my house where we have two showers and a bath running at 7am, but then I guess we could make the children stagger their showers! The pressure reading would be of use if you were planning a shower in the loft, otherwise no.

We haven't installed a VRC430 yet but hopefully it will be better than the VRC400 which was an awkward pig to use. I doubt the VRC430 is a match for the CM927 in terms of user interface, based on previous Vaillant offerings.

The fitment of the 430 should be in the house, the boiler fitment only saves a piece of cable and offers reduced control.

The VR65 controller does offer other benefits in so far as the boiler can manage and understand the cylinder loading, so on balance I would go for the weather comp. Sell the 927 on ebay and spend a couple of days reading the VRC430 manual. If it is like the VRC400 manual most of the important stuff will be missing.

When you get an installer to quote, don't tell them about your pressure/flow. See if they take readings unprompted. If they don't, they are a chancer.

Similarly, ask them to explain the design benefits of weather comp -you'd be shocked how many have no idea.

Finally, don't be surprised if the clever ones aren't the cheapest!

 

[Doctor Drivel]

I've seen Vaillant weather compensation discussed recently but want further opinions.

As a precursor to a loft conversion in an unextended 2 bed Victorian terrace, I intend to replace my S plan vented system (Potterton Profile 50e feeding 7 rads via microbore and 22mm gas supply throughout run; no TRVs) with a unvented cylinder and system boiler.

It will remain a one-bath property but I don't fancy a combi.

The mains is supplied by a 1in lead pipe which delivers a measured 27l/m off peak and c. 22 peak to kitchen and bath cold taps. I've not had the pressure measured.

I'm almost sold on having a Vaillant 618 and 155l Unistor connected via the VR65 control centre, but am dithering over replacing my Honeywell CM927 room stat (in hall) with a Vaillant VRC430 weather compensation unit. We do have an appropriate N facing external wall for the sensor.

Questions:

1) Should I insist on a pressure test (X bars..) from installer even though the flow rates seem adequate?

2) Would a very disruptive upgrading of the 1in lead supply pipe to 25mm plastic offer any improvement in flow rate (I doubt it..)?

3) What are the pros/cons of having the VRC430 weather comp. plugged into the boiler fascia - where it doesn't monitor room temp - or having it wall mounted in the hall, where it would monitor room temp?

The new boiler would be in the kitchen, which faces SW and gets lots of sun.

Thoughts from Vaillant installers (gas4you, simond..) very gratefully received.

cheers

A loft conversion? Look at this thread. Forget the old wives tales about combis, quality models are around that really perform. You really need a good decent to high flow combi. Look at this thread Take note of the Ethos, although other models are mentioned.

//www.diynot.com/forums/viewtopic.php?t=102568&start=15

 

[joncox]

Thanks Simon, very helpful. House is uniformly - but not well - insulated. Sash windows, no cavity wall, etc etc.