2 x 2-port versus 1 x 3-port diverter valve

[hfr254]

I have been away for a couple of days so missed the replies until now. The house is a large 4 Bedroom house. I checked with Glow worm regarding the use of the recommended 30 hxi boiler, Glow worm said because their boiler is a fully modulating boiler, over sizing will NOT affect the efficiency. since the boiler simply drops back on to its lower firing rate as and when required. Sorry guys but I'll take the word of Glow-worm themselves.

I will be fitting an automatic bypass, two valves one HW and one CH. and a glow-worm Climapro RF programmer / thermostat. I also intend to only fit TRV's on 80% of the 13 radiators.

What’s your thoughts on fast recovery cylinders?

 

[D_Hailsham]

The house is a large 4 Bedroom house.

Fine; but have you checked what size boiler you really need (EST online boiler calculator) or are you relying on the installer?

I checked with Glow worm regarding the use of the recommended 30 hxi boiler, Glow worm said because their boiler is a fully modulating boiler, over sizing will NOT affect the efficiency. since the boiler simply drops back on to its lower firing rate as and when required.

Correct,as far as it goes! But a boiler can only modulate between an upper and lower limit. If it can't modulate low enough, it goes into on/off mode. which is less efficient. The 30hxi will modulate between 5.3kW and 28.2kW.

If you house needs all 28.8kW in the depths of winter (-1°C outside) to bring it up to 21°C, then it will only need 5.3kW when the outside temperature is 17°C. Above that temperature, the boiler will stop modulating and run in on/off mode. But say you really need only 10.6kW in the depths of winter, then the boiler will stop modulating when the outside temperature reaches 10°C.

The first case is acceptable as the number of days when the outside temperature is between 17°C and 21°C is much fewer than those when it is between 10°C and 21°C.

If your boiler is considerably oversized, you could be running in on/off mode for 50% of the time or more.

 

[hfr254]

Comments from D_Hailsham noted and appreciated. I have since put the house through 3 heat loss calculators, the results varied from 17.5 to 19 kw for heating only and I assume about another 3 to 4 kw for HW. so that comes out around 21 to 23 kw to cover CH & HW.

I take your point about the lowest turn down burn rate but the Glow-worm site says the 24 hxi runs between 5.3 and 24 kw and the 30 hxi between 5.3 and 28.2 kw . even the 18 hxi only goes down to 5.0 to 18.6 kw.

So it would be touch and go whether or not the 18 hxi would cope, and would I be any worse off going for the 30 hxi rather than the 24 hxi

All help and comments very much appreciated

 

[Agile]

Sorry guys but I'll take the word of Glow-worm themselves.

Be aware that anyone earning £14-£20k answering phones at G-W is likely to be less knowledgeable and experienced that some of the business proprieters advising on this forum.

Its very unfortunate for you that you seem to think that all people advising you here are ignorant plumbers and therefore bound to be thick and stupid. After all they left school at 15 and plumbing was all they could do!

You have clearly not been able to use the heat loss calculations which meet the current energy saving recommendations as if you had done so you would have seen that they only require 2 kW extra to be added for HW.

If your calculations were correct then why are you unable to see that a 24 kW boiler would be more than adequate? In reality an 18 kW would probably suffice but then I dont know what your house construction, insulation and location is like.

Tony

 

[hfr254]

Oh How I love people with attitude, an axe to grind and a chip on their shoulder.
Lets address the dumb plumber accusation first, my brother RIP was a dumb plumber and he installed the original boiler in 1975. I left school at 15 with not one single qualification, but now at 63 I have a HNC in Mechanical Engineering and a BSc from the Open University, so I’m always willing to learn and get advice from the best source.

OK then , I will shift down and ask my installer to use a 24hxi, see I can take advice, That’s why I use DiyNot. Dare I ask what people think of the modern Climapro RF programmer/room stat.

Thanks to all who give advice without grudges? Once again thanks.

 

[D_Hailsham]

OK then , I will shift down and ask my installer to use a 24hxi, see I can take advice, That’s why I use DiyNot. Dare I ask what people think of the modern Climapro RF programmer/room stat.

I'm surprised nobody has queried your choice of Glow-worm products.

After all, now you have accepted our suggestions about the size of boiler, may be you will be open to suggestions about the make.

 

[Agile]

I think that slowly he is coming to see the benefit of the free professional advice we can give.

Many people do buy Glow Worm boilers however the general opinion amongst installers is that there are better boilers available from other manufacturers.

Popular makes are Vaillant with a usually three year warrantee or Viessmann with a five year warrantee in some cases. There are also some very good boilers from smaller manufacturers but they are not always recommended because of the unfamiliarity of engineers and the difficulty of getting parts if they should go wrong.

The most important aspect is that any boiler is installed on a clean system!

Tony

 

[hfr254]

Ok I'm open to sugestion. The reason I intended to go with Glow-worm was the 34 year old glow-worm boiler I still have that has never missed a beat, ever.

Second reason was that "Which" recommends the glow-worm hxi boilers, and also up there with glow-worm is "Vaillant". I am a little confused as to why you are now saying Vaillant are preferable to Glow-worm, I sent an email to Glow-worm last week with a question and the Vaillant technical department replied. so they are presumably the same manufacturer.

I am open minded, I just want a good reliable modern condensing boiler with RF controls.

 

[Agile]

I thought Which recommended the Baxi Duotec ?

Unfortunately Which does NOT do proper research! They tend to survey their own members who are mostly Groups AB and have too much money to spend so they are most likely to use a registered installer who properly cleans the system.

We see what our members find when they install the different makes and how repiable they find them.

The G-W and Vaillant brands are under the same ownership but some of the models are significantly different and most installers prefer the Vaillants.

Tony