Old regular boiler packed in - replacement ?

L_J_Silver

Our 34 year old Glow-Worm boiler has finally packed in and we need to replace it.

We have never had a combi before and three local installers have recommended this. Two said Worcester Bosch CDi 38 or a less expensive Baxi Duo-tec 40. The other said WB CDi 34 or Baxi Duo-tec 33. One said if we wanted another regular boiler then the WB CDi 30 Regular would be okay.

Our house has 5 bedrooms ,17 radiators and one bathroom with a bath and separate mixer shower.We use the shower rather than the bath. There is only the two of us now as our children have grown up and moved out.

We dont know a great deal about boilers and have never had to choose one until now !

We would be really grateful for any views on the recommended makes, size and type of boiler that may be suitable.

Many Thanks.

unclebulgaria

Those first few boilers are monsters!
Did they say why they had quoted such big KW's?
A 30kw combi will manage your heating easily with some to spare, its the hot water side of the install that would require bigger boilers. Have you had the incoming mains water pressure and flow tested at standing pressure and with a tap running, if so what was the result?
To take advantage of those bigger boilers you would need at least 2 litres per min more on the incoming mains pressure/flow than the boiler's rated for. i.e. if the boiler is rated at 13 litres per min hot water flow then you want at least 15 litres flow when it was tested at a tap.
Big boilers also require more gas too so could mean upgrading your gas supply piping. Has this been mentioned at all?

L_J_Silver

Hi unclebulgaria thank you for taking the trouble to reply to my post.

I think they recommended the size of boiler because of the size of house ie 5 bedrooms,17 radiators etc . The only testing i recall was running the cold water tap for a short time which they said was fine. As regards the supply piping it was mentioned that it would need to be upgraded from the existing 22ml to 28ml.

Also they recommended a new thermostatic shower as our existing mixer shower wouldnt work with combis.

As i said in my first post i dont know much about boilers and have never had a combi, they just seem so complicated to me !

So if we decided to stay with a regular boiler we wouldnt need such a powerful boiler ? And would we still need to upgrade the supply piping to 28ml ? .

tabath

Doesn't matter how many radiators you have. In fact for a house your size a 22kW boiler if they did them would be sufficient for heating purposes. As the OP said it is producing HW where you need the power and as you only have one bathroom something round 30 - 32 Kw should be fine. In a previous life I was a Qualified gas engineer so am not guessing about this.

L_J_Silver

Thanks for your comments tabath.

unclebulgaria

Johnny_L. wrote: »

Hi unclebulgaria thank you for taking the trouble to reply to my post.

I think they recommended the size of boiler because of the size of house ie 5 bedrooms,17 radiators etc . The only testing i recall was running the cold water tap for a short time which they said was fine. As regards the supply piping it was mentioned that it would need to be upgraded from the existing 22ml to 28ml.

Also they recommended a new thermostatic shower as our existing mixer shower wouldnt work with combis.

As i said in my first post i dont know much about boilers and have never had a combi, they just seem so complicated to me !

So if we decided to stay with a regular boiler we wouldnt need such a powerful boiler ? And would we still need to upgrade the supply piping to 28ml ? .

Upgrading the gas pipe on a conventional boiler depends on a lot of if's and but's and I would have to guess. It all depends on distance from the gas meter and how many bends and elbows are fitted to the gas pipe to get there and how big the new boiler is in KW. A 22mm copper pipe supplying any conventional boiler would usually surfice.
Make sure that any quote included them checking the flow properly if they advise a combi, running the water isn't good enough.

macman

The choice of a combi versus conventional boiler is down to you, depending on the house and your lifestyle, not your installer. Is the water pressure and flow rate even suitable for a combi-did each RGI who quoted check that?
A combi is not suitable if both bathrooms are in use at the same time. Also you can have no CH output when hot water is being drawn.

L_J_Silver

Thanks unclebulgaria.

The existing gas pipe has around 18-20 metres to travel from the meter to the boiler, i dont really know the number of bends and elbows. As yet i have only had one quote for a conventional boiler which was a worcester bosch cdi 30 regular.

I was hoping the existing 22ml pipe would be sufficient for the above boiler should we opt for a conventional one.

L_J_Silver

Thanks macman.

The only checking done by the RGI was running the cold water tap for a short while which they said was fine so i just assumed that it was okay. I cant recall us ever having any problems with this.

I do agree that it is our choice of type of boiler, the installers we have had just seemed very keen on the combi saying things like it was easier to install and cheaper.

I will listen to their advice but as you say will have to consider our lifestyle and may end up opting for what we have been used to !

unclebulgaria

Johnny_L. wrote: »

Thanks unclebulgaria.

The existing gas pipe has around 18-20 metres to travel from the meter to the boiler, i dont really know the number of bends and elbows. As yet i have only had one quote for a conventional boiler which was a worcester bosch cdi 30 regular.

I was hoping the existing 22ml pipe would be sufficient for the above boiler should we opt for a conventional one.

Hmm 18-20m is a long way in a straight line, are we talking ups and downs and alongs here or have you measured directly from the meter to the boiler?
What you have to remember is that if the boiler is under gassed after its installed then unless the installer is prepared to come back and put his hands up to underestimating the pipe sizing he's going to have to put it right. Its the installers responsibility to work out the correct pipe size. Conventional boilers don't run at the same gas rate as combi's so 22mm would probably suffice, depends on the size of conventional boiler.
If you have a large family and multiple bathrooms then perhaps a combi is the wrong choice unless you go for a 440 or 550 worcester floor standing boiler or equivalent. Combi's suit smaller households with one bathroom/shower, bedrooms don't come into it unless you have a mansion?. There are lots of if's and but's and preference has a part to play in your choice.
But please don't go down the route of an enormous combi as you dont need it unless you have fantastic water flow rates you want to take advantage of.
As far as losing your central heating goes when running hot water you wont really notice it unless you left the tap running for ages.

macman

Johnny_L. wrote: »

Thanks macman.

The only checking done by the RGI was running the cold water tap for a short while which they said was fine so i just assumed that it was okay. I cant recall us ever having any problems with this.

I do agree that it is our choice of type of boiler, the installers we have had just seemed very keen on the combi saying things like it was easier to install and cheaper.

I will listen to their advice but as you say will have to consider our lifestyle and may end up opting for what we have been used to !

So flow and pressure were not properly checked. A combi is indeed easier to install-and so the installer's margin may be higher.
Find another RGI who asks you what you want, rather than telling you what he would prefer to install.