Unusual system - usual problems! Loss of pressure

[coopersim]

My parents have an ongoing problem with their recently installed central heating & hot water system.

It is a vented hot water system and selaed central heating system, and comprises of:

2 x BAXI 100 HE Condensing boilers working in tandem
2 x 250L hot water tanks 450x1500mm (indirect)
50 L Expansion vessel
2 x 100 gallon cold water storage - rising main 22mm (flow rate and pressure unknown)
3 x salamander hot water pumps (mounted in the loft) delivering hot water to the bathrooms and kitchen.

The boilers are mounted in the loft spce, along with the cold water storage tanks and expansion vessel.

The pressure on the heating system drops over a number of days, this has to be constantly topped up to prevent the air reaching the boilers in the loft and them cutting out.

The expansion vessel has been checked for pressure and this is correct, there is no water present at the air refill valve.

there is no water present at the tundish from the PRV's on the boilers, also there is no water present at the system relief valves (there are two of these that drain in to a small tank, that then connects to the overflow after the PRV tundish, which continues to the outside) A bag has been attached to the overflow to test if there is any loss through this, the bag is dry

A very small amount of water has been noticed to be dripping out of the heat exchanger on one of the boilers, but is presently dry.

3 bottles of system sealer have been added to the system to try and prevent system water loss if it is a leak in the CH - however, I have been around the entire house with a moisture meter on walls, floors etc, and there is no sign of damp anywhere - the heating engineer of 40 years states that the system is loosing 5 litres a week when in use. The house is of cast concrete design, with CH pipes laid in floor channels, back filled with loose insulation material.

My questions are:

1. Is there anyway that the water could be leaking in the heat exchangers and being "driven" out by the intense heat here?

2.Is there anyway that the leaks could be internal to one or both of the hot water cylinders? Maybe the coil?

3. There is also a water softener, could this cause any problems in terms of introducing air in to the system?


Any suggestions to this ongoing and annoying problem most welcome!

 

[Softus]

B*gger me, 200 gallons of stored cold water - how many parents do you have?!

I'm curious to know why the installer isn't resolving this, if the system is relatively new.

Meanwhile, have you surveyed the house with the heating off and cold, so that no leaking water is evaporating before you find it?

 

[gas4you]

pressurise system to 2 bar, isolate boilers via ch/flow connections and leave for 2/3 hours. If pressure drops then you have a leak in system pipe work. I would not recommend using leak sealer at all.

When you say one boiler has a leak on the h ex do you mean it is visible when the cover/combustion chamber cover is off?

It sounds to me to be a leak in the pipe work under the floor somewhere as you cannot see any damp patches.

This unfortunately can be caused by the installer doing his job correctly and flushing out the system properly, without which your manufacturers warranty could have been void

 

[Softus]

pressurise system to 2 bar, isolate boilers via ch/flow connections and leave for 2/3 hours. If pressure drops then you have a leak in system pipe work.

Er, unless the isolating valves let by...

 

[gas4you]

good point, but trying to give simple answer that op can do himself. I am hoping that as install sounds new these would be working

 

[coopersim]

Would it be possible to change the configuration of the heating system, from a sealed system to a pumped system, by removing the expansion vessel and having a small open expansion tank above the level of the boilers? This would reduce the pressure on the pipe work, and hopefully avoid the need to dig up floors to locate leaking pipework?

Could anyone advise on the cons of this idea?

Many thanks.

 

[namsag]

Yes it can be piped as you suggest but the chances of the leak stopping now it is open and water escaping is very unlikely. And if left all you will do is allow fresh oxygenated water to come into the system through the header tank and this will result in rads etc corroding very quickly. Best to try and find the leak or repipe . It may be possible to isolate various parts of system to narrow down where leak is

 

[baxpoti]

2.Is there anyway that the leaks could be internal to one or both of the hot water cylinders? Maybe the coil

A process of elimination.....

Can you isolate the tank coils?

Can you isolate the boilers?

Is the heating system zoned, can parts be isolated?

Etc...

 

[coopersim]

Thanks for the replies, yes both the boilers and hot water tanks can be isolated with the use of gate valves, though I am not sure that these are 100% reliable in complete isolation??

I will suggest the above options and see how it goes, once again thanks for everyones time.