Fitted Propex - No water from hot tap - 4 hours and still stumped!

[johnfrosty]

Hi all.

I have bought a brand new Propex FJE10 (10 litre water heater). I fitted it into our new (gifted from relative) large LMC caravan.

I followed the instructions (which are limited both in scope and quality of English!) but can't get water from hot taps. Here's more detail...

I got all the water connections done and everything is water tight. I have not yet connected electric because I wanted to check the pipe system first (for leaks) and I want to run a fused switch/socket for the heater to isolate it on it’s own fuse. I assumed it should all work cold (without it being plugged in, but now wonder if maybe there's a pump inside?).

Once the fittings were all done, we struggled to get water through the system, both hot and cold. I ran the submersible Whale pump but struggled to get water anywhere. I assumed it was air in the pipes so we put a mains hose on briefly to purge the air from the system (our mains pressure is quite low here) and that worked nicely for cold, we got cold water coming strongly from all the cold taps in the caravan.

But we can not get water from the hot taps at all, even after doinhg the same thing and pushing water through the hot water pipes, coming out strongly at the hot taps.

The water tank appears to be full (it's heavy now). I don’t suppose turning the water heater on will be the solution? I can’t see how but maybe that’s what I need to do. I read in the manual that the system should be checked for leaks first, before powering the heater, so I assumed that means I should be seeing water from the hot taps even if it's only cold water for now.

I have attached a picture, not that it’s much addition to the explanation above! Any ideas would be much appreciated at this point! Thanks

(PS The system works by pulling cold from the on board tank (which is currently outside on the ground next to caravan as we are doing work inside), it runs around the caravan to under the bed where it has a Y splitter. One side goes to cold taps, the other to the water tank cold inlet. Then the hot pipes start at the hot outlet on tank and run in two directions (another Y splitter), one way to the bedrooom sink/shower, the other to the kitchen tap. I pulled out the old Truma system and have made no changes to pipework. That had two hot outlets and one cold inlet, Propex has one of each, hence the splitter).

 

[johnfrosty]

Update:

Perhaps almost solved. I spoke to Propex and they said to try removing the pressure relief valve. I did that, hey presto, water through hot water pipes, at all taps. Hooray! He said the pump isn't strong enough (it's pretty strong for a caravan!) to push the spring and let water into the tank. He said to remove the spring. There must be a reason for the spring to be there, so I am going to remove the spring and try to weaken it by nipping the end off bit by bit til it works as it should. Thought I would update the thread in case anyone else has a similar problem.

 

[Buckman]

Update:

Perhaps almost solved. I spoke to Propex and they said to try removing the pressure relief valve. I did that, hey presto, water through hot water pipes, at all taps. Hooray! He said the pump isn't strong enough (it's pretty strong for a caravan!) to push the spring and let water into the tank. He said to remove the spring. There must be a reason for the spring to be there, so I am going to remove the spring and try to weaken it by nipping the end off bit by bit til it works as it should. Thought I would update the thread in case anyone else has a similar problem.

Need to be careful as too much pressure may cause the pipes to come apart?

 

[johnfrosty]

Yes. I should have explained a bit more, especially for anyone who happens across this thread with same issue...

That valve they include in the box to fit on the cold inlet of the tank - It serves 3 purposes:

1. Non Return Valve - to stop hot leaving tank back through cold pipes
2. Drain Valve - tap to drain water from tank (with a small pipe coming off the nipple which goes through floor of van)
3. Pressure Relief Valve - most important function - So when water is heated and expands, it will auto bleed through the drain valve to relieve pressure in pipework.

 

[ProfJohnL]

I suspect the Propex unit is designed more for static or holiday home caravans where they have a mains water supply and of course a higher working pressure than touring caravans.

I am surprised your caravan pump isn't capable of raising enough pressure to open the 7psi non return valve.

It is necessary to have an NRV on the input to a storage water heater, as without it the contents and pressure of the hot tank can find its way into the coldwater feed piping.

It is also important to have an excess pressure relieve/drain valve to firstly provide relief if the pressure rises to far, and to allow the system to be fully drained against frost before off season storage.

I do not know the details of the combined valve you have, but if the NRV function can be disabled, but the pressure relief and drain features can be retained I'd suggest that is one step, but you will need to fit a NRV just before the drain valve in the cold water feed.

There are several manufacturers of suitable NRV's

 

[johnfrosty]

To be honest I don't think it's a pump pressure weakness issue, I think Propex are avoiding admitting it but the PRV is too strong. Long story short (and many conversations with someone at Propex), they changed the PRV they include in the box. The newer ones have a stronger spring and I suspect more than a few people have the same problem. he advised removing the spring inside the PRV which just seems ludicrous to me. So I removed the spring, nipped a few bits off it until it opened with the caravan pump pressure, and hey presto all working fine. They do actuallly offer to supply a different PRV (with weaker spring like the older ones) and I am sure that would do the same thing, i just hate waste so I weakened my PRV's spring and all good

 

[ProfJohnL]

That looks like a workable solution. And I'm glad you have retained some spring force to close the valve, as without the spring it could allow the the valves shuttle to relax to open and that would compromise the heaters operation reliability and possibly safety.