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Either way we get to a situation that the designed method of accommodating expansion has now gone.
Pressure cooker
When this happens, as stated earlier, after a draw off of hot water, say to wash the pots, enough water has been drawn off to reduce the temperature in the cylinder and with the tap off, you now have a sealed system. The cylinder calls for heat and the water starts to expand.
The pressure rises because it hasn’t got anywhere to go to and if the pressure reaches the set point of the combined T/PRV, typically set between 6 and 8 bar, water is ejected out of the system to prevent dangerous pressures being reached (this is a key safety feature of all unvented systems). This water passes into and out of the tundish that is normally located within the vicinity of the water cylinder. But, these cylinders are nearly always located in a cupboard with a closed door (let alone up in the loft).
Visible discharge?
The door is shut, there may be linen stacked in the airing cupboard, the homeowner doesn’t understand why the tundish is left in view (some tundishes are even tucked out of sight anyway by the installer due to space constraints).
Water starts to dribble out of the cylinder T/PRV, through the tundish and does so every time the discharge warm up cycle happens (as many as two or three times a day). On each occasion the water being dumped is warm, that means you have paid to warm the water up and then allow it to simply run to waste.
Checking for problems
Who actually does this? I cannot think of anyone I know that would regularly check to see if water is dripping through the tundish. Who has time to do that? But conversely, I know of people who have seen this water but because the tundish is doing its job (and allowing to pass into the drain without issues), they simply ignore it, they actually think that it’s supposed to do that because “it does it all the time” . Even when faced with the dripping water, homeowners don’t realise that its dripping because there is something wrong and just leave it dripping, wasting water and the energy needed to heat that water.
Alarming issues
What can be done to alleviate this situation? One way could be to educate the homeowners, the other is to encourage them to get their appliances serviced regularly, but none of these actually achieves measurable results.
BOILERS & WATER HEATERS
For most of the UK’s boiler market the PRV point of discharge is located outside the house and water dripping out of the PRV is left to simply drip down the wall
This is one of the reasons I have been working on a solution for the last five years and have come up with a product that alerts the homeowner in a way that makes sure they take quick action.
Sensing a result
hotun detect, is a simple, clip on, battery operated (three-year life with low battery warning), water detection and temperature sensing alarm unit. It gives an audible and visual warning that water is present in the tundish, and like all alarms, draws immediate attention to get something done about the situation. Even if the unit is re-set, it will simply go off again the next time the PRV discharges.
The benefits to the installer
Let’s say the installer has fitted the alarm and they have put their contact details on the alarm unit. The first time the it sounds, the homeowner (or installers customer) rings them to ask to have the problem fixed.
Given that the alarm has a diagnostic function of temperature giving different audible signals (one, two or three rings in quick succession) this give the ability to triage the problem over the phone. The installer arrives at the property with a good idea of what is wrong and is now going to get paid to carry out the repair.
The customer is happy because the problem is fixed and they are not going to waste water or let the heating system be at risk from corrosion potentially damaging the boiler.
Environmental impact
The cumulative effect of managing water going out of the T/PRV to drain will have an important benefit of the conserving of valuable water resources. We need to use this water for the purpose it was intended and not have it simply run to drain just because the homeowner does not realise the importance of water dripping through the tundish or out the pipe through the outside wall.
Visibility
One final thought for all appliances (boilers and water heaters) fitted in lofts, who would ever notice or even go up into the loft to check to see if the hot water cylinder is loosing water through the T/PRV via the tundish? It’s not going to happen, and that is why fitting hotun detect, makes sense.
Typical boiler in loft installation (Picture by Chris Smith)
www.heatingandventilating.net
January 2021
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