Sizing of new boilers

I'm in the process of looking at replacing two existing Vaillant VC GB 242 EH system boilers (around 10 yrs old). I'm currently looking at the Vaillant or Worcester Bosch range. I want to re-calculate the required boiler size in the house (I have the individual room measurements) in order that I'm 100% sure we get the right sized boilers. Is there a piece of software/website that allows me to enter the measurements to get the correct BTU/KW required?

Thanks

First we have to wonder why you would want to replace those so early.

If you're happy with the heating, use radiator sizing charts to add up the output you need to supply, and add an allowance for heating up (say 10%) and also for pipe losses (also 10%) then add an allowance for the HW cylinder, which can be considerable and vary a lot between systems.

Thanks for your response ChrisR.

We have had problems with one of the Vaillant boilers for some time now. Basically, the flame reset switch on the front of the boiler would continually pop out (varying from every few hours to every few days) causing the boiler to shut down. As both of the boilers are in the attic, sometimes we didn't realise it wasn't working. Having already spent £1,000 trying to get the boiler repaired with one CORGI plumber, he couldn't fix it (even though he wanted to replace part after part) and the boiler wouldn't even fire-up after he had finished. I recently took out a maintenance contract on the boiler to reduce some of the costs. The company replaced the flame supervision circuit board, and the boiler fired-up and appeared to work without fault. A few days later, the reset switch started to pop out again. The maintenance company came back and diagnosed it as a air-pressure switch fault. The part was ordered and they came yesterday to fit it yesterday. Once fitted, they turned on the boiler and it blew the flame supervision circuit board, again! They tell me the fuses are ok, there is 240v coming to the boiler, but there is no output to the ignition device. Vaillant won't come out because of inadequate access/no hand-rail. If this boiler can't be repaired, I guess the only way forward is to replace it and as it would be a condensing boiler, it would make sense to do both boilers.

Any ideas?

Thanks

rip it out and take to the nearest tip. It really makes me smile when people continue to throw good money after bad! Of course the boiler repair lads would love you to keep it I have spoken to people who have spent 2k on trying to fix and patch up a dying system.

Spend the extra cash and buy something reliable. Get a handyman to sort out proper access. Will you get another vaillant....

When we had the boilers installed just over 10 years ago, they appeared to be the best available on the market. Vaillant have told me that they were a 'new generation' of boiler, but obviously Vaillant have improved the reliability, efficiency and performance of their newer boilers.

The access problem is because the cyclinder is in the middle and blocking access to both boilers. To make matters worse, we redoing one of our bathrooms and we have noticed there is a crack that goes from the ceiling below the attic, through the screed, down into another room below. As the cyclinder weighs over 1 tonne when full, it looks like the weight on the lintels is too great causing this crack. We're outside our NHBC guarantee now, but I am trying to get quotations for a Megaflo Indirect to be installed in our airing cupboard.

From research on here, Vaillant and Worcester Bosch seem to stand out. Just a matter of finding the right sized boilers I guess.

I am trying to put together some form of plan and parts cost. We have recieved a quotation of £12,500 to replace the boilers and cyclinder. That's a lot of money as we won't save that on the better efficiency if the new system lasts 15 years.

@ htgeng - I think this is a lesson for anyone that has a plumber/boiler person out to fix a boiler that he/she is not familiar with. We got to the stage with him that he had bought all 3 PCBs for the boiler, at just over £100 each, and he wanted to replace them all. I finally called it quits with him when I asked Vaillant for a copy of their servicing manual and saw what the PCBs did and their circuits. I am still thinking of claiming some money back off him as when he started the boiler worked, although it was resetting regularly, but when he finished the boiler wouldn't even fire up. Going through what he had done, all I can see is that he cleaned the boiler, serviced it and added an inhibitor to the system. Not exactly £1000 worth of work as far as I can see

Buy a Buderus system boiler, there is no other gas fired boiler to touch it for long term ease of and low cost maintenance.

Leave the working vaillant in situ. Keep the old one for spares.

I can email you an example of a two boiler system using Atag boilers. Sounds like you are looking for a high end system. If you wanted to email me more details I would be happy to help. Bucks is just about in my catchment area if you wanted an alternative quotation with Atag or Viessman boilers.

htgeng said:

I can email you an example of a two boiler system using Atag boilers. Sounds like you are looking for a high end system. If you wanted to email me more details I would be happy to help. Bucks is just about in my catchment area if you wanted an alternative quotation with Atag or Viessman boilers.

Click to expand...

Have to agree the Atag or the Buderus are the bees knees.

It amazes me how quickly the new boiler brigade will want to remove a solid boiler (which the VCW is) to replace it with a new super efficient boiler.

While there is nothing wrong if the boiler in question is being replaced if it is duff, beyond repair or parts are not available. VCW is none of these. What the poster is experiencing is unknowledgeable part changers. The ONLY way to repair an appliance is to get to know how the boiler operates, follow the operate sequence and then locate point of defect. Clearly this has not taken place.

WRT new replacement boiler controlled by 'black boxes' and superchips, these appliance will soon (my view only) require PCs, crt scopes and other fancy test gear to analyse and fix (often replacement of very expensive PCBs). Other parts like modulating fans and what not will not be in the same price bracket as the VCW spares.

I will keep my VCW running as long as possible. Have lagged the loftspace, have a HW cylinder (might replace that with a UV cylinder), combi supplied water in kitchen, one zone upstaris and onother downstairs.