Do I change to a condensing boiler?

housebuyer143

I moved into a new house and it has an old glow worm boiler which looking into it further appears to be non-condensing. It's 20 years old so my probably not that efficient, but would it be worthwhile changing it to a condensing system boiler? I have a tank in the airing cupboard which I want to keep.

At present it is costing me 71p an hour to run the heating and I am on a tariff which cost 4.2p a kilowatt of gas 😱😱 I am terrified for when my tariff ends as it could be costing close to £2 an hour to heat my home.

Are new condensing boilers that much more efficient? Is it worth the spend?

[Deleted User]

Are new condensing boilers that much more efficient?

Yes. There is already an ongoing thread on this very subject.

https://forums.moneysavingexpert.com/discussion/6403765/worth-getting-a-new-boiler

Getting an installer at this time if the year may be a challenge! Don’t add a new boiler to a 20 year old heating system without having it properly cleaned. New boiler warranties are invalidated for sludge.

Astria

Personally I'd have a full survey by someone competent. New boiler, possibly new radiators as they are probably older than the boiler and not efficient either and maybe even replace some pipework depending on whats currently installed - you want the water returned to the boiler to be as cold as possible once it's gone through your entire heating system.

diystarter7

Astria said:

Personally I'd have a full survey by someone competent. New boiler, possibly new radiators as they are probably older than the boiler and not efficient either and maybe even replace some pipework depending on whats currently installed - you want the water returned to the boiler to be as cold as possible once it's gone through your entire heating system.

OP
If you are poss going to do as above, get all round new pipes as well. Most people get them flushed but best to get the whole thing done but if you are not fully settled in yet.

Rodders53

housebuyer143 said:

At present it is costing me 71p an hour to run the heating and I am on a tariff which cost 4.2p a kilowatt of gas 

Using Sums (aka maths) that means, when first on heating up the house it's burning 17 kW of gas per hour.  = 17 kWh consumed.  Or is that just what it displays when the burner is on?

Modern Glow Worms come in output ratings of 12, 15, 18, 25 or 30kW.  Even old ones like yours would have been made with similar ratings.  So your gas consumption roughly matches the 18 kW one?

In all likelihood it will start cycling the burner on/off relatively quickly ....  with it being more off than on as the comfort temperature is reached in the home. It'll be going either flat out or off as it's a simple boiler (more modern ones can reduce the heat output to more closely match the heat demand from the house radiators).

Does the boiler have a pilot light permanently on or an electronic ignition?  Pilot lights are very wasteful of gas so that will be a (better) reason to change boiler.

Look more at the daily totals of gas used over the time you've been in the house:
1.  On days when only hot water has been heated
2.  On more recent days when you've had some heating on.  

Keep a log of how long you've had heating on and temps set on thermostats and any TRVs in different rooms.  Turn down bedrooms / unused rooms with TRVs? etc.,.

Once you start logging your daily gas use you may be pleasantly surprised (or even more alarmed, but I hope not).

Read up the OTHER threads here where the same question has been asked... There's no one size fits all answer.  New boilers are expensive and any payback period will be long, no matter what a kWh of gas costs.

tacpot12

The old radiators might be efficient at the lower flow temperatures that a condensing boiler needs to operate at, but you won't know this until they are surveyed by a competent engineer as stated by Astria. Most radiators and pipework are large enough as they have been oversized for other reasons. 

housebuyer143

Thank you all.. The glow worm is 18si so is 18kw. At the moment I have only been putting it on for an hour due to the cost but the smart reader reads out 71p for the first hour and then 50p into the second, so it might be better to have it on more than an hour at a time, although not much! 
It seems to be running constantly when it's on, as in the boiler sounds like it's working hard. 

I read some other posts and have turned down the heating temp to 65 degrees and hopefully the water still gets hot and if so will keep it at that and look for a saving. 

The house is only 20 years old so the rads are the new kind and we have proper sized pipes. I imagine it will benefit from a flush through though at some point. 

I'll keep a log as @Rodders53 suggests and see if I can reduce it down anyway. The pilot light doesn't seem to be on all the time, so that's good at least. 

Water currently burns between 10-15kw a day, and that's on for an hour a day, but I'll try and reduce that to 30 mins and see what happens 👍

BUFF

The 18Si had a seasonal efficiency rating of 76.8% when new - not the worst but certainly nowhere near  the modern mandated ~90%. However, it probably isn't performing at that level these days & it probably doesn't have modern controls either (which can make a surprising difference if used properly).

Because your boiler is non-condensing you won't really see much of a saving imo from turning the heating flow temp down to 65C.