Over the years I’ve been confronted by with the argument that its better to hold on to the old cast iron heat exchanger boiler rather than change it for a new high efficiency (HE), low water content, condensing boiler. So, I thought I’d lend my opinion as seasoned engineer and human being!!
A customer of ours came to us recently with a problem about the controls on his system, these were cheaper controls and we recommended a new set of controls from a more expensive but trustworthy brand. During the course of our visits and conversations the topic of boiler replacement was brought up as he has a 20+ year old floor standing 48kw Ideal Mexico boiler, not currently causing a problem but he was interested in perhaps changing the appliance now rather than wait for it to fail at some point in the future. However he had read an article in the Telegraph suggesting that it would be better to keep his “good old” boiler rather than paying for a “less reliable” modern condensing appliance.
Please see link below to one of the journalists other articles.
Obviously a rather conservative view being taken on “keeping the old boiler” which one is to expect I suppose from the Telegraph (just my opinion!!)
Being one who likes to dabble in a little maths and physics, I am an engineer after all, I set about deciding whether actually they had a point. I can see a certain logic in keeping the old, less efficient appliance, there’s less to go wrong, after all its just a cast iron water jacket, gas valve, burner and thermostat. Nice, simple and until parts are no longer available then why not keep it chugging on? And yes, because new boilers are more complicated, then problems can occur more often, but their intricate controls make them more fuel efficient so it’s a bit of a paradox.
But in this case I could see one flaw, in that having done a heat loss calculation for the whole property, the boiler only needed 24kw of heat input to meet the heating and hot water requirements, half of what the current boiler is providing. So assuming that the current Ideal is only 65% efficient or thereabouts, then not only is 35p in every pound spent on gas going up the chimney but nearly half what is being used is potentially wasted.
Obviously, we are a firm of heating and plumbing engineers so it’s in our interests to sell and fit boilers, but we are also humans and have a conscience so supplying the right information to the customer to make their own decision is very important.
Needless to say the customer has opted for a brand new Vaillant Ecotec Plus 30kw sealed system boiler combined with new controls, magnetic filter and a full power flush of the heating system.
I know what your thinking, why 30kw, you said 24kw input needed! Well yes a 24kw would do, but the customer wanted belt and braces so opted for a larger boiler. And here’s where the clever new generation of condensing boilers really steps up over the older cast iron boy’s. A new HE boiler will modulate it’s heat output based on the flow and return temperatures, knocking back the output at the burner if necessary or ramping it up. Certainly with the Vaillant products you can even specify the maximum output, so if its a 30kw boiler and you only need 27kw you can tell it to do only 27kw.
I’m not saying you need to rip out and throw away your old Ideal Classic or Potterton Netaheat, but if your about to spend £300+ on a 20+ year old boiler then it might be worth considering not throwing good money at bad. There’s a lot to take into consideration and getting the right installer to help make that decision is definitely a good start.
Note: In the article below the author states that the life expectancy of a condensing combi boiler is 5 years, in my experience that’s complete rubbish. A good Vaillant combi serviced annually on a well cleaned system should last at least 15 years. But beware of cheap boilers, they will give you long term headches.