Mixer bath taps/shower initially have no hot water

[UKRay]

Hi all, Sorry if this already appears on the forum, but I am unable to see the posting which I was sure I made @ 16:15 today and have not seen any responses so I guess that I failed to post it correctly.

OK, my first posting herein although I have often turned to this excellent forum for information and help.

My problem: I have just installed a thermostatic mixer bath tap/shower unit for the outlaws which is working “intermittently”. It was a simple job - apart from the usual issues of tight space to get a spanner to the tap retaining nuts. - I had to install the unit since the old folk were having problems getting the fine adjustment required to obtain the correct temperature on the existing non thermostatically controlled unit. Once I turned the cold & hot water stopcocks back on the thermostatic control did not appear to let the hot water through the mixer. To check there was hot water in the system I turned the sink hot tap on. Soon after the mixer tap delivered the hot as required as set on the thermostat. The tap (bath filler) & shower feed subsequently worked fine on Friday. I had a call on Saturday saying that hot water was not being delivered, only cold. Again I turned the sink hot tap on and again the hot water started to flow ok as it did for several further attempts shortly afterward. I made a further check today and again no hot flow. The basin trick did not seem to work this time so I opened the kitchen sink tap & the hot again flows fine.

My thoughts – wrong or right - are that there is either an air lock or water lock that reaffirms itself after a period of time. Or it could be the obscure way the water pipes are configured in the house.

Does anyone have any suggestions on how to resolve this issue?
Thanks.

 

[dreadnoughtheating]

Ray, is the cold supplied direct from the 'Mains' at say 2 bar? AND the hot from a storage tank in the loft by any chance?

If so, at best a Pressure Reducing Valve MAY offer an acceptable solution, certainly non-return valves would be required under Water Regs.

Or, you may have to re-run the cold-water supply back to the cold water storage tank to ensure equal pressures on both sides of the valve.

All too common an issuein the UK I am afraid. Did the valve suplier ask you what sort of water system you have before selling it to you?

DH

 

[UKRay]

DH,
Thanks for the rapid response. I guess that what you have described is the case. As a self taught but untrained amateur with no qualifications in plumbing, I guess these are the sort of things I fall fowl of. I just picked up on the original pipe work connected to a plain set of mixer taps. The cold is obviously supplied from the mains as it has the higher pressure (although I have not measured it I would not be surprised that it is 2bar or more). The hot is fed by the CH system & ultimately from the loft tank and is at a much lower pressure.

Since I purchased the mixer from the internet I was not asked what system it was for. So I guess it is my fault for not researching it thoroughly, although the description did not mention the possible need for equalising the pressure with pressure reducing or non return valves.

Thanks very much for the help. I will go out and get the appropriate valves on the morrow.
Cheers
Ray