Got to spec a combi boiler

[Dannypipe]

Hello all.

Just pricing a job, and I've got to do something which I guess for many is bread and butter work.....fit a combi boiler.

However this just isn't the market I'm generally in, and I haven't fitted a combi boiler since the scrappage scheme!

(generally I fit and upgrade systems with stored water on larger properties, so unvented cylinders, thermal stores and h/o boilers.).

So I was just doing a bit of research for flow rates, and allthough the house I'm fitting it in only requires 7KW for heating needs, I was going to fit a 24 KW combi.

From what I've read, flow rates are crap, and in winter I might even be getting phone calls as it takes two days to fill a bath. Never concerned me before, but since I'm doing this for a friend of a very valuable client, I don't want to get it wrong!


I just want to know opinions on good combi's and whether I should spec a 28KW instead of a 24 to give the hot water a better flow rate?

Or fit a combi with a resevoir of H/W?

Anyway opinions from the combi installers gratefully recieved.

Ta,

Danny

 

[SimonJohns]

I would go for the larger capacity boiler. Depends on gas run and ££££

I have a 35kw in the house. Fantastic Hws. But I've been to houses with a 24 and your there all week

 

[dancinplumba]

as simon says, go for biggest cust will let you if good flow and pressure, when they have good hot water they will thank you for it, boiler is down to
price
imo 🙂

 

[Pssst]

Or just fit a system boiler and retain HWST

 

[Dannypipe]

Yeah, this is my concern. The existing gas run is a pig and makes no sense. Right round the side of the house, and then up to the loft before dropping down to a first floor bedroom.

When all they had to do was punch it virtically up and into the bedroom directly. This will mean more pipe on show on the front of the house though.

I think I'll spec 28 minimum and offer 35 as an option.

What about stored water combis.

I've repaired quite a few and fitted a Vailant years back. Always seemed quite impressive, but then a lot more dosh for that little bit of storage. Any opinions on these?

Whats your prefered combi?

 

[Dannypipe]

Or just fit a system boiler and retain HWST

I suggested this, but she wants rid of the cylinder to free up some room in the spare bedroom. Plus she's moved from a flat with a combi and I couldn't talk her out of it.

There are other reasons, she wants a lodger to share the bills, and thinks it's less complicated with a combi.....

Can't believe its been so long since I fitted one.

I did one during the scrappage scheme, and before that it was years. I just don't fit em very often!! Never really thought about it before.

 

[dancinplumba]

🙂 intergas 🙂,atag, vaillant ok if you have good flow and press carnt beat big combi imo, no storage heat loss

 

[dancinplumba]

baxi/pott ask gasman ?? 🙂

 

[bennygas]

To be honest Danny, I think it'd pay to be mindful of the quality of service afforded by the incoming cold main in terms of available pressure and flow rate. If the cold main's rubbish, sticking a massive combi in ain't really going to do much but drive up the cost of the installation (e.g. appliance cost and gas supply sizing), and it may then leave you in the position of having to explain yourself out of an awkward situation. A 35kW combi's not going to deliver the sort of service it's capable of unless you can give it enough water in the first place. Me personally, I'd check what the cold main is likely to give you in terms of pressure and particularly litres/min, and then gauge the size of the boiler according to that. If the cold main's shockingly poor, I think you need to ask the question as to whether or not a combi is the best or only solution, or whether works could be feasibly undertaken to improve the service from the cold main. I agree with simonjohns on the 24kW note - hws can be pitiful, maybe 9-10 litres/min at 35 degree rise, whereas if you can get up to something like a 35kW, you're into the realms of 14-15 l/m which is pretty respectable. Hopefully, if the cold main's respectable, you'd be able to get away with a decent sized combi, but I think you probably want to be looking at 28kW+ (around about 11-12 l/m) for anything like a reasonable service. hope that shed's a bit of light.

 

[bennygas]

blimey how many people posted while I was typing that?

 

[dancinplumba]

bit like sizing for unvented, regards flow and pressure, you only get out what you get in
imo 🙂

 

[Dannypipe]

Tested cold main flow rate, didn't bother taking the pressure. It was +20 litres per minute. Peak time too at 8am.

I'm concerned that in the winter to flow rate might be crap with the temp rise being more crucial.

I serviced a boiler a couple of years back, a WB. The customer called me back. The flow rate was just not enough. So I double checked it. Checked the temp rise and flow rate with my weir cup. It was fine. Explained to customer that their boiler was working fine. They'd moved in during a very hot summer and now it was a very cold winter The water temp of the cold main was probably 10oC colder. He couldn't get his head around it, and said he wanted a new boiler. I never got the job. Think he thought I was full of bleep!

So many thanks for all the advice.

I'll go for a 28KW and warn her that she won't get as good a flow rate as she will with a 35 but that would be a lot more money. I'll not spec a 24 as it's just not going to cut the mustard.

Feels like I'm back at school!!

 

[bennygas]

ere, dancin, u like that big vaillant storage combi? I fitted a couple when they first came out. it's like hanging a washing machine on the wall!!! I remember the first one i did was under the stairs in the basement of this old house, I was nearly cryin' - the std flue was JUST about long enough to pass through the exterior wall (over 2 feet thick, made of granite). By the time I got the thing on the wall I was thinking this thing better be worth it. I finished it, hot water was stellar, well impressed, to the point of thinking about putting one in my gaff. Then about a week later I ended up having to get vaillant out to fix the thing. think they went back 2 or 3 times. don't know what the outcome was, I don't really think they knew to be honest. you ever had any problems with them?

 

[bennygas]

summer winter variations do seem to be much more pronounced on smaller combis, I guess a bigger one can compensate for the cooler cold main temperature more effectively. At the end of the day danny, if you give the customer as much relevant info as required in order to help them make a decision on the size of the boiler, together with the pitfalls and costs associated with each case, you're covering yourself really - the ball's back in their court so to speak. they're the ones making the decision, you just need to give them the options together with the costs. I'd plump for a quote on a 28 and something bigger, but I'd be clear to them that the bigger the boiler, the more likely it is that they would need to upgrade the gas to suit (who's to say the gas is big enough for a 28 as it stands?). that way in the somewhat unlikely event that if they have a 28 and then come back to you saying that in winter the hw is poor, you can turn round and say, "well I did give you the option..."

 

[Dannypipe]

Yeah true. The gas p/w aint big enough as it stands and I have allowed to uprate it.

I'll give her both options I guess, you're right.

I take on board what you're saying. 28 isn't going to be amazing either.

It seems nuts putting a 34KW boiler into a two bedroom house. It goes against the grain of what I generally do which is to size the boiler to suit the house.
If I was her, I'd stick a 12kW system boiler in, uprate the cylinder to an unvented and have great hot water flow rates.

You can take a horse to water, but you can't make them swim.

 

[TBServices]

Don't forget to see what the range rate goes down to on the boiler if the heating demand is only 7kw.


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[tamz]

Even in a 2 bed house i'd still spec as a min a 28 unless they are on a budget. Saying that if they only have a shower they will never notice the difference if it was a 24. Horses for courses. We all know what is best but sometimes you just have to compromise.

 

[Dannypipe]

Funilly enough, I also have to price to fit a shower in the bathroom as she doesn't generally bath.

But........I don't want any future problems down the line. I'm pushing her towards a 33KW Baxi Duo tec, but have given her the option of a 28kW too.


Given her the option of the WB as everyone seems to ask for one, and budget boiler, a (don't laugh) Biasi Riva Plus 28kW.

Four boilers on one quote. Think I've covered all options!!

 

[TBServices]

Plumb centre are doing the Vaillant EcoTec pro 28 for £725+ inc flue. Gotta be better value than the WB/Baxi.

I hate worcesters *spits*


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[Dannypipe]

I hate em too, but everyone asks for them. Cheers for the heads up.

 

[Mike Jackson]

I used to like Worcesters, I've even got one in my own gaff (40CDi combi in a two bed terrace), but I'm not so keen now with the way they are putting sales above quality and service.

My boiler of choice is now Atag and the 325C combi is one of the most cost effective 35Kw combis on the market. Worked out about £300 cheaper than a Worcester 30Cdi.

 

[TBServices]

I hate em too, but everyone asks for them. Cheers for the heads up.

I know they do. It's strange. I just explain that they're trading on a reputation that was built years ago and no longer deserve, and I'd rather fit something else. Obviously the customer is always right, But I can normally talk them out of a worcester lol


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[Pssst]

I suggested this, but she wants rid of the cylinder to free up some room in the spare bedroom. Plus she's moved from a flat with a combi and I couldn't talk her out of it.

There are other reasons, she wants a lodger to share the bills, and thinks it's less complicated with a combi.....

Can't believe its been so long since I fitted one.

I did one during the scrappage scheme, and before that it was years. I just don't fit em very often!! Never really thought about it before.

You see this illustrates the main reason for ripping out perfectly good storage systems and fitting combis..."i want an extra cupboard".

Hardly based on sound engineering but the truth is that when it comes to decisions in the home...women are the initiators and final arbiters. Trying telling a woman all about flow rates and efficiency and she will glaze over. All she wants is another cupboard to fill with carp and in return,she will suffer higher bills and carp baths and put the nation at risk in wasting precious resources such as gas and water !

An example..only this weekend came home to drip drip through ceiling. ELCBs had been flicking off for a couple of days but just blanked it 🙂

Inspection panel off cupboard,found naffed satchwell duoflow valve lagging out.

Thinks...>>talk of combis and stuff...nah..off to screwfix and bought danfoss y plan control pack for 80 notes. Spent best part of a day on a bit of plumbing and rewiring to allow full control (previously had randal 103 TOC clock)..now have fully pumped independant channel 5/2 day bliss.

OH keeps moaning as she is used to clanky old 103 that she can flick round at will. Boiler..the trusty spacesaver rated to a measly 38k btu/hr.. Thats BTU not Kw 🙂

 

[cdodds2004]

dont stick a combi store in,, if you fitting one of these i always think its just a cheap alternative over a unvented system.

main eco 25. dhw is 10.4 i think litres a minute
main eco 30 dhw is 11.8 - 12 i think.

if im worrying slightly about flow rates i usually stick the 30 in as its not much more money,

flow rates for most 24-25kw combis are sub 11 and 25-30 are 12 ish

 

[Whn1]

dont stick a combi store in,, if you fitting one of these i always think its just a cheap alternative over a unvented system.

main eco 25. dhw is 10.4 i think litres a minute
main eco 30 dhw is 11.8 - 12 i think.

if im worrying slightly about flow rates i usually stick the 30 in as its not much more money,

flow rates for most 24-25kw combis are sub 11 and 25-30 are 12 ish

Im pretty chuffed wih the mains. Been fitting them for about 5 years now and they're still going strong..