Truma Combi Heater

[Past_it]

Hi All
I have a van which is 9 months old with a Truma Combi water heater/room heater.
I have no problems with the system as such and it seems to do everything it should ….
Now the bad news.
When using the onboard shower it seems to cycle the water from hot (60 degrees) to cold in about 5 or 6 second intervals no matter where the mixer tap is positioned.
Because we know this, it is simple to move away from the shower head during the hot phase of the cycle but would be dangerous if we had the grandchildren with us.
Has anyone else had this problem or is it a known problem in the design of the system?

 

[Martin_E]

It could be that the pressure switch needs a tweak, when you start pressure is up, then tails away until the pump kicks in again, pressure then builds as it should, pump switches off, pressure drops, hence the temp variations. By adjusting the pressure switch you will get an even pressure and no peaks and troughs

 

[ProfJohnL]

Hello P.I.

Martin's suggestion may not be enough to cure the problem on its own. The reason the temperature fluctuates is the pressure in the hot and cold pipes work is not fully synchronized because the hot water heater has an air cap (which it needs for safety) which acts like a pressure reservoir and the cold system doesn't.

When the pump runs, it raises the pressure of both hot and cold at the same time, but when the pressure reaches the pressure switches threshold, the cold water stops being delivered but the hot system continues to deliver because of the residual pressure in the tanks air cap, so you get a surge of hot water.

This problem is recognised and you can get a 'surge damper' to fit to the cold system pipe work.

 

[Past_it]

Thank you all for your replies, much appreciated.
Of course if this is a know issue why isn't it rectified by the manufactures?
Can you tell me where I can aquire a "surge damper" for my system.
Thank you all again for your input and interest.

 

[ProfJohnL]

Surge dampers should be available from or through your local caravan dealer

 

[chrisbee1]

The Surge Damper should be fitted as close to the water socket as possible.

Depending on the pipe work fitted, the surge damper will connect using a 12 mm Whale Quick Connect Plumbing Fitting (Equal Tee) to 12 mm pipe work or Stainless Steel Hose Clips to 10mm pipe work.

Surge Damper (WS7205)

Whale Equal Tee (WU1202)

 

[ProfJohnL]

if this is a know issue why isn't it rectified by the manufactures?
Can you tell me where I can aquire a "surge damper" for my system.
Thank you all again for your input and interest.

The reason why this fix is not standard fit, is it doesn't happen with every installation, its a combination of normal manufacturing tolerances such as the sensitivity of the pressure switch, the angle or length of a pipe or the individual performance of the pump that can just upset the balance of the system. So yes the problem is known but its not always going to occur.

 

[Gafferbill]

Past_it........you do not state which caravan you have.
If it is fitted with the Whale IC water pump control unit then........

this topic on another forum may be of interest.

 

[Past_it]

Good News .....
I finally rec'd an email from truma and as they suggested if there was a restricting washer in the shower head make the hole bigger etc.
I enclose the email from Truma:-

I have consulted with one of the engineers and respond on their behalf.
The surge damper is self-calibrating and should not need to be adjusted, what is needed is more flow to the shower. Set the shower us as if you are showering and then go and listen to the pump, if it is cutting in and out we then need to try to increase the flow to the shower. You need to check in the shower head and see if there is a reducing washer in there, if there is then you may need to make the hole in the washer slightly larger till the pump is running continuously.

There was a washer with only a 3mm hole in it ......

Needless to say all is well and the shower is working very well.
Thank you again for all your replies.

 

[ProfJohnL]

Hello Past It,

I'm glad you have a resolution, but it may not be the total solution for two reasons, The first is you will end up using more water, and secondly if you try to restrict the flow by the shower tap, you will end up with temperature surges again!

I'm intrigued now:- Truma's response states "The surge damper is self-calibrating and should not need to be adjusted."

Exactly what did you ask them to produce that response?

 

[Past_it]

Hi ProfJohnL
From your previous posting suggesting I should invest in a 'surge damper' I examined my system and realized I already had one fitted.
My dilema then was, had it gone faulty or did it need adjusting (it had a fine adjustment on the front)
I then emailed Truma explaining my problem and also asking if the 'surge damper' needed adjusting.
And you have their reply .... All this for a penny rubber washer.
I read all the info supplied with my caravan and none of this was mentioned.
All I can say is than goodness for Practical Caravan. and its forum members.

 

[ProfJohnL]

Ah now I understand.

 

[Martin_E]

Prof,

The Truma surge damper has been around for a long time, you don't see it in many vans though, probably due to cost, they cost somewhere in the region of £90 + & are indeed self calibrating by electronics.

Truma also do a self calibrating pressure switch that automatically does the same as the Whale pressure switch.