faulty thermostatic shower valve? All aspects of plumbing questions and answers, help, tips and information

[chris_on_tour2002]

hi,

hoping on of you folks could confirm my diagnosis of the following problem. doubly important as it's another job for the mother-in-law!

fortunately for me i didn't install the shower which was put in about 3 years ago. the builder supplied it and it was probably cheap - can't ascertain the make or model and no receipt was furnished and he says he doesn't have it now. which i feel is irresponsible, i assume he would have needed it for tax purposes and should still have it and should be available to exercise any guarantee. but there you go.

shower has stopped running warm (stone cold) unless the bath hot tap is running (fed from same pipe) the water coming from bath filler is roasting hot but the shower only gets luke warm.

the system is a megaflow, a large tank (not sure of size but pretty substantial) and blistering mains pressure - never actually measured it but it is substantial. so both hot and cold sides are at mains pressure. i'm certain it's not an airlock. the hot feed comes from directly below the bathroom into a tee where it splits to go to the shower and the bath filler. not huge runs of pipes, perhaps 4 metres from tank to shower and 6 metres to bath tap.

could be a blockage in the pipework, most likely at the gauze filter in the shower valve. but i'm more inclined to think that it's a faulty thermostat? just curious as to why it would only run warm when the bath tap running.

the reason it's such an issue is that i need to cut an access panel in the studwork wall in the upstairs landing in order to get access to the concealed shower valve. not a problem but i wanted to see if anybody on here might be able to suggest an alternative diagnosis before i go hacking walls to bits to change the unit - especially if it turns out to be unnecessary!

many thanks,

chris

[stoneyboy]

chris_on_tour2002,
Can't explain the bath tap/shower feature but try swinging the temperature control with the shower on from full hot to fully cold at least 30 times, it could be the thermostatic cartridge is scaled up. If this fails your next stop is to see if there is a filter in the inlet side.
end

[stoneyboy]

chris_on_tour2002,
Can't explain the bath tap/shower feature but try swinging the temperature control with the shower on from full hot to fully cold at least 30 times, it could be the thermostatic cartridge is scaled up. If this fails your next stop is to see if there is a filter in the inlet side.
end

[James1000]

If you can get the cartridge out and then turn the supplies back on again with it out, at least your be able to tell if there is an obstruction in the pipe work.

[chris_on_tour2002]

yep, there's no doubt about it the valve has to come out. i suspect that stoneyboy is correct, most likely scaled up at the gauze/filter on the hot side. it is in a hard water area and i'm sure that the taps don't have filters.

i still find it odd that some hot water will get through when the bath hot is run, i'd have thought the opposite would apply as the running water would cause a pressure drop in the pipes, effectively increasing the pressure of static water in the valve.

hey ho, better get the pad saw out :)

cheers guys