Fitting a new condensing boiler into an older system: What do you need to consider?

Boiler replacement projects aren’t as complicated as you might think, and you could be making significant savings in being proactive with your dated system. Believe it or not, there are ways and means of integrating new condensing boilers into existing systems and pipework, without risking contamination of the primary boiler circuit or loss of performance.

Separate the old from the new
Yes, it’s true that most high performance condensing boilers need to be installed as part of a sealed system, but even if this isn’t required, it is worth separating the new from the old to get the most out of the new boiler.

Granted, converting an open vented system to a sealed system can be tough, with potential leaks from old pipework fittings to consider, and potential corrosion if water from an old system gets into the brand new condensing boiler. Fear not, however – there are ways to avoid these issues.

The easiest way to get over this issue is to leave the existing system open vented and separate the boiler primary circuit using a stainless steel plate heat exchanger. Adding a plate heat exchanger to the mix ensures a safe and protected primary circuit for the new condensing boiler and reduces the risk of corrosion to the existing system at the same time.

Keep debris out
The heat exchangers in condensing boilers have become more sophisticated over the years and manufacturers have created designs which deliver greater outputs and efficiency from more compact exchanger units. However, these often have small water ways which can be easily blocked by large debris. Using a strainer/filter/dirt separator can protect your unit from debris that has not yet been flushed from the old system.

Expanding your savings
Where plate heat exchangers have been installed, the expansion vessel can be sized to accommodate the expansion of water of the small primary circuit to save on both cost and space. However, the filling arrangement will still need to comply with Water Regulations relating to the size of the boiler and the property – typically fluid category 4.

Finally, the plate heat exchanger effectively becomes the heat source within the new system so you need to consider the positioning of the open vent and cold feed in relation to the existing heat pumps.

Final thoughts
Although, at first sight it may seem like daunting task, fitting a condensing boiler into an existing system is achievable and can bring huge benefits when done correctly. It is worth taking the time to consider how a new boiler can deliver its full range of expected benefits despite being integrated within an older system.

Pete Mills, Commercial Technical Operations Manager at Bosch Commercial and Industrial.