The thermal oil Feroline U in Boiler is not gaining the desired temp of 240 Degrees. We have physically measured the temp using digital thermometer at a distance of 20 cm where the boiler temp sensor is installed. 40 degrees are lost in 20cm insulated area. The boiler is well insulated with Rockwool & oil quality is good (recently tested).
There are a couple things that could be going on, but most likely it has to do with how and where the temperature is measured rather than some sort of unknown heat loss. People are being critical in the comments, because the two measurements (based on the info given) should be nearly identical.
Seeing your replies in the comments, I am assuming both your temperatures were measured with the same measuring device, placed between the insulation and the metal pipe/vessel, and given time to reach equilibrium.
I assume A is your vessel and B is your outlet.
- Is B in fact the Outlet and not the Inlet? It is sometimes easy to mistake the flow through a plumbing system. Things are also not necessarily labeled correctly. It is very possible B is the Inlet to the heater and this temperature difference is the heat that is being delivered to users as planned. This is the most likely scenario with the info I have.
- Have you checked temperature B in different locations about the diameter? Maybe the flow is all to one side or there is rust/scale near the measuring location.
Have you checked temperature A in different locations on the vessel?
How close is point A to the heating element? (not sure of the energy input type, but the location/proximity of the electric heating element or heat exchanger will make a big difference. This is also a likely scenario.)
How close is A to the inlet? (this is where the cool oil returns in a closed loop system) (this is more likely to make A colder than B, but something to think about as well)
Other things to consider is that the steel thickness at B may be thicker or the insulation may be thinner. This results in your measurement being closer to ambient temperature than the the measurement at A. When we place a thermometer below insulation we are making the assumption that the insulation is much much more resistant to heat flow than the metal. Most the time this assumption is true, but it is something to consider when looking for accuracy.
If none of those items help you track down the issue please include info like flow-rate, energy source, energy users, etc.
If the equipment sensor is in a well, which it should be, remove it and put it in boiling water. Now put the equipment sensor in cooler water and check temperature. This will confirm span and accuracy, assuming all readings check, for the equipment sensor and indicator system. While performing the above take readings with your portable thermometer also. Record and compare the readings. Draw valid conclusions based on the data.