Faulty cylinder stat

[Teggs]

Wonder if you could shed some light on a problem I have. I have a combi boiler that feeds an unvented hot water cylinder (don't ask me why). Last night I found that there was no hot water from available from the cylinder.

When I turn on the heat or hot water the mid-position valve opens and closes accordingly so I don't believe this is the problem.

Today I turned up the temperature on the cylinder stat, the two-port valve appeared to open (making me think this isn’t at fault). The flow and return pipes from the cylinder soon warmed up, however after a while the boiler cut out as if the water had been heated to a suitable temperature. The temperature was set at 65 degrees C on the stat but the water from the taps was only lukewarm. If I turn the dial to 75 degrees C I here a click, the boiler then fires up again.

Is it usual for a cylinder thermostat to become faulty? I’ve checked the wiring diagram and the twp port valve appears to be linked to the two port valve, am I right in thinking that this tells the valve to close when the water is at the required temperature?

I it helps my set up is:

Baxi Bahama combination boiler
Grunfos 15-50 pump
Honeywell mid position valve
Protea unvented hot water cylinder
Sunvic 2 port valve (sitauted by the cylinder)
Honeywell programmer
No roomstat

Many thanks,

Terry

 

[doitall]

Let me try and explain.

Combi will heat water all the time it works, more offen than not it don't, so to give you hot water, it has become commen practice to connect the combi to the kitchen and utility, then have a cylinder to supply the rest of the house, however this runs off the heating circuit with the 3 port valve and not the hot water side.

it also gives you hot water when the boiler retires.

Unvented cylinder should be wired from the thermal cut-out through the 2port to fire the boiler and open the 3port turn the pump on etc

 

[doitall]

part 2,

thermal link opens the 2 port, which allows the system to heat the cylinder provided the cylinder stat is calling for heat and the boiler is programmed on heating, room stat will shut the heating side of the 3port if up to temperature.

nearly confused yet

 

[corgigazza]

is there a gate valve on the return from the bottom cylinder connection this may be shut/blocked

 

[doitall]

just read a bit more of your question

There has to be a room stat or something to control the heating side of the flow share valve, Assuming you mean flowshare i.e. 3port.

 

[corgigazza]

some cylinders (Elson silver?) not heard of protia? have a blending valve on the top outlet these go faulty and mix to much cold water in with the hot, the adjustment is via red control knob on side of brass blending valve, you can strip @ clean these vavles reassemble with silicone grease

 

[htgeng]

it also gives you hot water when the boiler retires.

nicely put!

 

[Teggs]

Sorry, yes there was a rom stat as it turns out.

From what you guys have said it sounds like the cylinder stat is not to blame? If it isn't the stt what else could it be? The thermal cut out device does not seem to have tripped, at least I haven't had to reset it.

Yours,

Tery

 

[doitall]

Still tying to work out what you actualy have it could just be not wired up right in the first place.

Do you know if it was fitted by a compitent person with a ticket and has he signed your log book

I'm in London all week so on the 3G mobile office card so connection is not always good but I will try

 

[Teggs]

Funnily enough the log book han't been completed. It's a barn conversion but I'm not sure who fitted it as I wasn't the owner from new.

The system has worked up until Saturday night.

I spoke to a merchant today who confirmed that Protea are no longer. Apparently they have been taken over by Titan whose spares are the match for my cylinder.

Can anyone confirm why a cylinder stat would have 2 cables running from it? Is one for the motorised valve and one to switch the boiler on and off when the specific water temperature is achieved?