Boiler pressure dropping

Anders_Loidis · Post by **Anders_Loidis** » Mon Oct 28, 2024 3:33 pm

Since the heating has been put on this month, the pressure on the boiler keeps dropping slowly but surely to below 0.75 bar, at which point the boiler does not fire up in the morning. Over the years I've had to top it up a couple of times a year, now it needs topping up weekly.

My question is this, does a consistent pressure drop mean a faulty boiler or a leak somewhere on the system. Or potentially either?

I've had a quick look around the house and no valves are weeping, and no visible wet patches anywhere.

The boiler is an Alpha CD35C installed in 2007, with 11 rads. While everyone tells me Alphas are cr*p , we have never had a problem with it. Fingers crossed, it's never "broken down", although it has always been serviced annually by the original fitter.

Any thoughts /advice much appreciated.

dewaltdisney · Post by **dewaltdisney** » Mon Oct 28, 2024 3:50 pm

The first thing to check is the pressure relief valve letting by. Try to find the valve and look at the outlet for drips.

DWD

gas4you · Post by **gas4you** » Tue Oct 29, 2024 6:30 pm

Then get the expansion vessel checked for the right pressure setting.

Anders_Loidis · Post by **Anders_Loidis** » Wed Oct 30, 2024 9:45 am

Thanks guys. Just a quick question for the uninitiated, when you say "check is the pressure relief valve letting by" do you mean the two taps underneath the boiler that I turn to fill the system? If so, these are not weeping. They do when I fill ,but stop when closed again.

dewaltdisney · Post by **dewaltdisney** » Wed Oct 30, 2024 10:16 am

A pressure relief valve is a means to allow a boiler system that gets over pressurised for any reason to open and allow water to escape down a drain tube often venting outside but sometimes direct to a drain pipe. Over time these can weep or if they have discharged and debris can get trapped at the seal allowing a slow leak. The expansion vessel that Dave mentioned is another thing that can cause this issue as there is a rubber bladder in a vessel that can lose pressure so more water needs topping up to fill the void caused. Sometimes pumping this up (it has a tyre like Schrader valve)can rectify this but if it continues as an issue an external expansion vessel can be added more cheaply than replacing the one in the boiler.

Sadly, your boiler is at the end of its life, 17 years is a good run as most boilers do 12 to 15 these days. Any money you spend repairing it will only extend its life a short time until the next fault. Best to get quotes for a boiler exchange, the new boilers are far more fuel efficient so there is a payback scenario to consider. The warranty periods can be very good too so you could have a five year loan to fund it during this period.

Probaly not what you wanted to hear.

DWD

Anders_Loidis · Post by **Anders_Loidis** » Mon Nov 11, 2024 11:37 am

Just a follow up question guys.

I have checked the pressure relief pipe outside, and the decking is soaked, which suggests a continual leak from the pipe. (not rained for a few days so easily visible).

In the process of getting quotes but being time of year, lead time of several weeks being mentioned.

My question is this, can I keep filling it up to keep it going, and is it likely to just "pack up" suddenly. Could I possibly get through to the summer? Appreciate your help. Cheers

dewaltdisney · Post by **dewaltdisney** » Mon Nov 11, 2024 11:45 am

The boiler guy can check to see if there is a reason for the PRV release. It sounds like debris on the PRV seal allows a slow leak. Topping up will be okay but it will dilute any inhibitor in the system so you might want to ask the engineer to add a fresh dose as he will have to drain down to fit the PRV anyway.

DWD