Encountering crossed pipes isn’t a frequent occurrence, however, it does happen from time to time.
Despite being a relatively straightforward problem to put right, the various issues that this can cause will add extra work to a heating engineer’s already busy schedule.
Martyn Bridges, director of technical communication and product management at Worcester, Bosch Group, has identified a series of simple checks that will help ensure that these issues do not arise later down the line.
1. System flow and return
Crossed system flow and return pipes will generally happen either because a property’s original boiler was piped the wrong way round initially. Nowadays with combi boilers, sealed systems and bottom opposite end fed radiators, it isn’t as crucial as it used to be.
The return temperature for combis is typically 20°C lower than the flow, and most boilers now feature a sensor on the flow pipe within the boiler to monitor this and ensure it heats up as required. If the pipes are reversed, the sensor will record the lower temperature and could compensate to make up the difference. This can result in unwanted noise, or overheating and inefficiency.
Some boilers may also have a sensor on the return, meaning that if pipes have been crossed, the boiler will detect that the return temperature is higher than the flow temperature and enter a blocking code to signal a fault.
As well as checking the flow and return temperatures during the commissioning process, it’s important to ensure that the existing pipes are installed the right way round. Using different coloured tape is a simple yet effective method of differentiating between the flow and return pipes.
2. Mains hot and cold on a combi boiler
Crossed hot and cold water pipes may simply be down to incorrect piping to the original boiler – resulting in the cold mains being piped into the hot outlet and vice versa – or, a basin or sink may have been piped the wrong way elsewhere in the system.
Many combi boilers will not fire if the cold mains inlet and hot water outlet connections are piped incorrectly, so the main symptom in this case would be no hot water being delivered.
Nowadays, combis also have a temperature sensor on the hot water outlet, meaning that if the cold mains and hot outlets have been installed the wrong way round, depending on model, the boiler could fire but will continue to fire, however, it will do so at maximum rate.
Again, the first port of call should be to check that the existing cold mains and hot outlets are correctly installed, and different coloured tape can also come in handy here too.
During the commissioning stage, it’s important to check the cold and hot water temperatures at the outlets of the property. This can be done by isolating the cold main inlet at the boiler and opening a hot water outlet. If everything is correct, then there should be no water running – if water continues to run, then the pipework is crossed.