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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 3591
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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when I run the hot water the system pressure drops and hot

Customer Question

when I run the hot water the system pressure drops and hot water does not reach temerature .Could this be a fault on the differential valve DHW ?
Submitted: 5 years ago.
Category: UK Plumbing
Expert:  Rick Ridley replied 5 years ago.
Hi I am Rick, UK Plumber, and I specialize on Boiler problems, need a little more info to say, is this a combi boiler or an unvented cylinder, Rick
Customer: replied 5 years ago.
Hi Rick it is a Baxi Combi Instant 105e
Expert:  Rick Ridley replied 5 years ago.
OK when you run hot water you say the system pressure drops is that correct? can you say what the pressure is before and during running hot water, Rick
Customer: replied 5 years ago.
when running the hot water the system pressure drops from just over 1 bar to practically 0 this is not a sudden dramatic drop but over a period of a few minuets and then the system requires topping up
Expert:  Andrew Smith replied 5 years ago.
Hi my name is XXXXX XXXXX lets see if we can get you sorted in the shortest possible time. Your plate to plate heat exchanger could be blocked? Can you check whether the pressure relief valve (15mm copper pipe going through the wall to outside below the boiler) is dripping or running outside? Has this been getting gradually worse?
Customer: replied 5 years ago.
No this is dry
Expert:  Andrew Smith replied 5 years ago.
If the boiler is not discharging outside, then you will have a leak. Do you have any damp patches anywhere?
Customer: replied 5 years ago.
no no damp patches point to note that if heating is on then the pressure is fine this only happens when drawing hot water
Expert:  Andrew Smith replied 5 years ago.
If on heating does the pressure go back up again? Depending on the model and where the pressure gauge is connected into the boiler, if there is a slight restriction in the plate to plate heat exchanger the pressure from the pump can make the system pressure in the boiler decrease.
Customer: replied 5 years ago.
no I have to recharge the system
Expert:  Andrew Smith replied 5 years ago.
There is only two ways for water to leave the system - a leak or it blows out the PRV. I would encourage some investigation, under floorboards etc.
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 3591
Experience: Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
Andrew Smith and other UK Plumbing Specialists are ready to help you

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