HW Cylinder getting too hot

[EngineerDave101]

I have recently moved in to a house with oil central heating.
There is an MA1 mid-position valve, HTS3 cylinder thermostat and a Lifestyle LP522 programmer.
The problem is that the water in the cylinder gets too hot.
The cylinder thermostat is working correctly - moving the valve to the CH position when the tank temperature is satisfied.
I would have expected the pipework from the valve to the tank to reduce in temperature somewhat, however it continues to be exceedingly hot - the same as the CH pipework as far as I can tell.
The tank thermostat is set at 60 degrees and the boiler thermostat at about 75 degrees.
I note that the lever on the side of the valve indicating its position is not fully home at either the HW or CH positions but assume this is normal.
Is there a problem with the valve, i.e. is water bypassing the closed HW port and continuing to heat up the tank, or is something else going on?

PS I am a new member and very please to be on board.

 

[kris]

Couple of things possibly. The cylinder stat will be making and breaking but the sensor might be wrong. It's set at 60deg but it might be asking for a higher cutout. Have you tried checking the pipework when the programmer is on hot water only and once stat comes up to temp measure temp of water... Or put it onto CH only and see if coil pipes heat up and that will test the 3port valve...You can use touch. Or if you have a differential temperature reader.. If the cylinder stat is gone new ones are cheap enough.

 

[wild nomad]

Ummm does sound like a cylinder thermostat issue. If it's only just occured it's unlikely to be a wiring problem. However it's well worth checking nothing has come loose since cylinder cupboards are often used to store towels and sometimes wires get pulled loose taking things in and out of the cupboard.

Turn your programmer to central heating only for a while just to let the port valve move into position (assuming it does) then turn it all off for a while to let things cool down a bit. Then turn your cylinder stat down as low as it will go.

Turn the programmer to hot water only....

1) If the boiler comes on straight away with the stat turned low it would suggest there is something wrong with the stat and it has jammed at a high temperature or the over heat sensor has tripped and needs resetting. If it's a reset then you need to investigate why it tripped in the first place. Again possibly a dodgy cylinder stat or a jammed port valve as you suggested. Also worth checking that the stat has a good contact with the cylinder. These can often work loose.

2) What should happen is nothing. Slowly turn the cylinder stat up and at some point this should turn on your boiler and pump as the stat 'calls' for heat. Set it to 60oc if it came on before this. Also you should hear your port valve move position. If you don't hear it or suspect it's not fully engaging then it could be jammed in the HW open position (Two Port) or jammed in the mid position (Three port) in which case the radiators would come on with the hot water. Eventually the boiler should stop as it gets up to temperature. At this point measure the water temperature at the closest hot water tap to the cylinder or shower if you have one connected. Whatever your stat is set to the water should be a bit lower or equal to it.

Also, as Kris says above, checking the pipes either side of the valve is a good idea. Leading into the cylinder side of the valve the flow pipe should get hotter with the hot HW ON and cooler with the HW off and Heating ON. Again, as already mentioned by Kris, Cylinder stats are cheap to replace.

I am presuming you have a vented system with tanks in the loft and all that btw?

I may have missed out a few other tests and apologise if you have already done a few of the above but this is a starting point. Hope this helps

Oh, and just thought. Some systems have immersion heaters attached to the cylinders as back up. Check that this hasn't somehow turned on if you have one.

P.S. Welcome aboard!

 

[EngineerDave101]

Couple of things possibly. The cylinder stat will be making and breaking but the sensor might be wrong. It's set at 60deg but it might be asking for a higher cutout. Have you tried checking the pipework when the programmer is on hot water only and once stat comes up to temp measure temp of water... Or put it onto CH only and see if coil pipes heat up and that will test the 3port valve...You can use touch. Or if you have a differential temperature reader.. If the cylinder stat is gone new ones are cheap enough.

Hi kris,
Thanks for your comments.
As you suggested, I found a thermometer and checked the actual water temperature at the sink - 55 degrees! - not near boiling point as I had expected.
Nevertheless this confirmed that the tank thermostat was correct.
Regarding the hot pipework, I have reflected on that, and now consider it unreasonable for pipework physically connected, not to be influenced by the temperature of adjacent pipework, after all copper and brass are excellent heat conductors.
I'll do some more tests over the weekend, but for now I have convinced her indoors that there is no fault.

 

[EngineerDave101]

Hi kris,

I followed your advice and got hold of a thermometer,measured the water temperature at the sink – 55 degrees – not nearly boilingpoint as I had expected; this tends to show that the tank thermostat is workingOK.
I have been mulling over the pipework temperatures andnow consider it likely that hot pipework adjacent to the pipe to the tank wouldaffect that pipework as well, after all copper and brass are excellentconductors of heat. So although the pipework to the tank is hot, that does notnecessarily mean there is hot water passing through it.
Anyway I think I have done enough to convince “herindoors” that there is no fault, and will do further test at the weekend.
Thanks again
David

 

[EngineerDave101]

Hi wild nomad,

As you see in reply post to kris I had overestimated the water temperature.
I guess the fault was at my previous house where the temperature was not thathot - all comes down the initial settings i.e. boiler thermostat setting, cylinderthermostat setting, proximity to boiler, cleanliness of pipework, etc.

As I said I'll do some more tests at the weekend using your post and let youboth know.

Thanks again.
David

 

[stevetheplumber]

i would run heating only from cold and see if the motorised valve is letting by

 

[Boilerbud]

Remove two screws take head off try to move spindle by hand. Will probably be siezed up.