Baxi 28he combi pressure?

[commando3]

I have a Baxi platinum 28he combi boiler and recently it has been losing its pressure.
I have called out several different engineers now but they have all failed to fix the problem.

I have followed some advice found on this website and from other sources and I believe the problem is now a leak somewhere between the boiler and radiators but I thought I would run this by you just in case something has been missed?

So far - the expansion vessel has been replaced and repressurised. The heat exchanger was replaced. The PRV was replaced.
There is no signs of any leaks within the boiler.
The inlet and outlet valves were shut off and the boiler pressure monitored over 3 hours- there was no pressure lost.
When the valves were turned back on the pressure dropped by about 0.3bar.

The system was then repressurised to 1.5 bar and then the hot tap opened. The pressure drops to about 1.2 bar whilst the hot tap is running. When the hot tap is closed the pressure rises back to 1.5bar.
The heating is then turned on. The pressure drops again to about 1.2 bar immediately before rising up to 1.7 and holds at that.
There are only 3 double radiators in the house and a heated towel rail. I have checked all the valves etc. There are no signs of any leaks anywhere. They all heat up very quickly.
After turning the heating off the pressure stays the same for about 45mins but slowly losses presure over 12 hours.
There is no signs of water from the prv pipe outside.
There was a small drop of water coming from the Magna Clean lid but that was tightened up.

Am I right in thinking that the probable cause of pressure loss is a leak in the pipework between boiler and radiators?

 

[gigz]

The pump kicking in will make the pressure fluctuate on this boiler (instantly goes down when pump goes). I think you need to lift a few boards. You could add a leak sealer but personally would only go down that route if i couldn't access the pipes (i.e. Under screed/laminate). Have you checked the spindles on your rad valves ?

 

[Stadan20]

By heat exchanger do you mean the plate or the main ? Reason I ask is if main is split the water will go into condense pipe , shut off flow and return and leave for a couple of days . If pressure drops its the main heat ex . If it doesn't it's on your system , bear in mind if you shut flow and return off you will have no heating

 

[commando3]

Thank's guys for your suggestions.
The plate heat exchanger was replaced recently. The gas engineer who last looked at the boiler said there was no sign of any leaks in the main exchanger.
I have already closed off the CH valves and observed for any pressure drop. Thankfully there was no pressure drop which has led me to believe there is a leak in the pipework between the boiler and rads.
The pipework has been buried in concrete so I think this is where the leak is. I checked the rads for leaks but no sign of a single drop of water.
As suggested- I have now put in some sealer this evening. I had to put it in via the towel rail then I repressurised the system.
I note there are mixed views on using this sealer by it's worth a try.
Failing this working it looks like I'm going to have to put some new pipework put in but this time not in the floor. It will have to go down a corner of the room and along to the rads.
I note that on the Sealer instructions it says it takes up to 24hours to work. Can the CH be turned on during this time? It doesn't say on the instructions.

 

[gigz]

Yes.

 

[muggles]

Yes, most leak sealers need the heat to work properly, and they need the boiler to be on so that they circulate around the system

 

[commando3]

Many thanks.
Should i let the heating run for a few hours so the sealer can circulate?

 

[muggles]

Yes

 

[commando3]

Many thanks for your help guys but I've managed to find the cause of the problem.
As suspected I was right about the leak being in the pipework. The boiler suddenly wasn't holding any pressure after 30mins.
In my kitchen there is wooden floor stuck down on concrete. I put my ear to the floor near the rad and moved around inch by inch and then I suddenly heard water gushing. I homed in to where it was loudest and marked the spot. Then I went out and bought an oscillating saw and cut the wooden flooring and removed the planks to reveal a channel in the concrete with a wooden lid.
The lid was in sections so I undone the screws and lifted the lid to find a hole in one of the 22mm pipes. Bingo!!!!!
Being that the pipe is laid flat the difficulty was repairing that section but what I did was to cut the pipe from above with the oscillating saw . It went through it like a hot knife through butter. I then cut it again about 15mm thus removing the hole. Luckily there was some play in the pipework that allowed me to fit a 22mm pushfit connector.
All is now sealed and the boiler repressurised. No more pressure drops.
I haven't closed the opening yet in the floor as I want to dry out that channel and to finally make sure there's no leak from that pushfit joint.

 

[Agile]

If you could see the hole then I would have soldered it as that's the easiest solution if it is possible to drive the water out of the pipe with air.