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When a boiler dies it’s normally at the wrong time of year, typically when it’s cold and you’ve spent all your money on Christmas. However, you’ve been saving up for this moment, right?
Boilers are usually one of the more expensive household appliances you’ll have to replace with typical gas boiler replacements ranging from £1700 to £3500. With an external oil combi boiler however, the expense can be substantially more than a gas equivalent.
Coming from ‘the city’ and never having had to replace an external oil boiler before, we weren’t really prepared when our 15 year old our Worcester Bosch 18/25 Heatslave decided to call it a day. It started to lose pressure with a leak from an unknown source. A local heating engineer investigated the problem and explained it would be uneconomical to repair so we were left with the unenviable task of finding a replacement.
Over the next couple of weeks I spoke to a handful of heating engineers and got a range of quotes in. Pretty much two models kept recurring, the latest generation Worcester Bosch Greenstar Heatslave II External 18/25 Combi Oil Boiler and the equivalent Grant Vortex Pro 26 Combi Oil Boiler, both similar outputs and prices. This is where my naivety showed in thinking it was a £2k job, when the first quotes came in. The prices were varied, ranging from around £4000 to a more eye-watering £6000 for a full installation. As you can see, and this is what surprised me, the starting price for an oil boiler is higher than the top end price for a gas boiler!
The more expensive quotes tended to be from Worcester Bosch or Grant aligned heating engineers who wanted to supply the boiler themselves. Brand agnostic quotes were cheaper based on fitting a customer-supplied boiler, at the expense of losing the included warranty for using an official registered/approved heating engineer. However, these warranties can typically be acquired later on, with conditions attached.
The Worcester Bosch Greenstar Heatslave II (£3431) unit itself was more expensive compared to the Grant Vortex Pro (£3150), a difference of £281. Bizarre as it may sound, I decided to steer away from the accredited installers as they were significantly more expensive. I wanted to make this as cost efficient as possible, but without cutting corners.
Why I chose the Grant Vortex Pro vs the Worcester Bosch Greenstar Heatslave II
After much research on various forums, websites and suggestions by OFTEC registered local heating engineers I settled on the Grant Vortex Pro. Why? Not only is the actual unit cheaper, I got the impression through my research that non-affiliated but biased-through-experience engineers preferred to install and work on Grant boilers. On paper, the stats are very similar; both ‘A’ for heating and ‘B’ for water and both in the 92%+ efficiency rating.
Grant Vortex Pro vs the Worcester Bosch Greenstar Heatslave II Specifications
| Grant Vortex Pro | Worcester Bosch Heatslave 2 | |
| Warranty (Years) | 2 | 2 |
| Width (mm) | 658 | 640 |
| Height (mm) | 945 | 950 |
| Depth (mm) | 754 | 770 |
| Weight (Kg) | 206 | 154 |
| Output (Kilowatts) | 26 | 25 |
| Output (BTUs) | 9000 | 8500 |
| ErP Space Heating Efficiency | A | A |
| ErP Water Heating Efficiency | B | B |
| Flow Rate (L/min) | 17 | 18 |
| SAP Seasonal Efficiency | 91.71% | 89.2% |
| Sound Pressure Level | 50.6 dB | 56 db |
| Fuel | Oil | Oil |
| Mounting | Floor | Floor |
However, Which? does rate the Worcester Bosch brand higher. The Which? reviews of these models of Grant and Worcester Bosch really only rate the brand (mid seventies percentage for Worcester Bosch and low sixties percentage for for Grant) and not the boiler itself. It does tip a nod towards Grant being the ‘engineers favourite’, but not so much the customer’s favourite (favouring Worcester Bosch). Again, this is for the brand and not the model. So one has to take Which? ratings with a pinch of salt for these particular models at the time of writing.
Costs
The brand registered installers were at the top end of the quotes. The main difference between the two registered installation offerings were that Grant’s came with a maximum of 5 years warranty whereas the Worcester Bosch was 7 years. To get the equivalent independent fitting of a customer-supplied boiler, which averaged at about £650 inclusive of VAT, the price for the full installation with maximum available warranty was as follows:
| Grant Vortex Pro 26 | Worcester Bosch 18/25 Heatslave 2 | |
| Boiler | £3150 | £3431 |
| Magnetic Filter | £154 | £154 |
| Fire Valve | £42 | £42 |
| Fitting & Commisioning | £650 | £650 |
| Extended Warranty | 5 years £330 | 5 years (free) |
| Total | £4326 | £4277 |
Interestingly, the Worcester Bosch worked out £49 cheaper as the 5 year warranty is free if their magnetic filter (Greenstar Magnetic Filter) is fitted. With Grant you have to pay £330 to get 3 years extended warranty on top of the 2 years standard, and you also have to have a magnetic filter installed. You could use a non-Grant filter (Worcester Bosch need you to use theirs) which may make up the difference in price but I’ve done a like-for-like for a fairer comparison.
So, even with the marginally cheaper cost of a Worcester Bosch installation we went with Grant purely on the basis of it being the main recommendation as detailed earlier. Maybe the marketing helped a bit e.g. the patented stainless steel construct of the heat exchanger seemed to be a unique selling point and probably explains the substantial 52kg weight difference. Built to last? I hope so!
Where to buy the Grant Vortex Pro VTXOMCOMBI26 External Oil Boiler
Both Grant and Worcester Bosch external oil boilers are available from mainstream suppliers like Screwfix, Travis Perkins, PlumbNation and City Plumbing. We chose City Plumbing as the price was amongst the cheapest, free delivery and also local South West branches. Obviously, Screwfix are more ubiquitous but they are not specialist plumbing suppliers so, rightly or wrongly, I gave them a miss on the basis that City Plumbing would be able to give me better and specialised help in the event of something going wrong. At 200 kilos I opted to get the free delivery which was painless, the delivery chaps even got it to our door (meant to be kerbside).
Now that it is installed, what do I think?
Well, it’s obviously nice to have hot water and heating for a start! It seems marginally better at heating the hot water, especially in the upstairs bath and shower; the old Heatslave would struggle a bit. Its a little bit noisier than the Heatslave it replaced although on paper, less noisier then the new Heatslave. Heating wise it copes very well with the ten radiators in our house. Only time will tell if I’ve made the right choice.
I did have chance to dismantle the old Heatslave so as to take it to the local recycling centre (after keeping some of the more expensive copper piping for myself!). I discovered the reason for its ultimate demise. The rather expensive water tank had rusted through so badly at the top that it had become permeable. I’m rather hoping the Grant Vortex Pro doesn’t have these same rust issues and can match it and possibly outlive it! Based on the cost and the average 15 year lifespan of an oil boiler, it’ll cost me £24 a month to save up enough…I’d better get saving!