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Dry Well Thermostat Introduction

(also known as the  Pipe Stat,  Aquastat or Immersion Pocket Thermostat).

A dry well thermostat is supplied with the H2 panel, it is a very important link in the control system indicating the status of the solid fuel boiler, either the boiler is up to working temperature (58°C) or it is not, it controls the following functions

When the solid fuel boiler is not in operation it is isolated from the rest of the system, thus preventing the automatic boiler from wastefully heating the solid fuel boiler.
When the solid fuel boiler is first lit, or in slumber mode it is prevented from sharing its output with the rest off the system until it is up to working temperature, this keeps condensation and resulting corrosion in the fire box to an absolute minimum, extending the boiler life.
When the information that the solid fuel boiler is up working temperature is relayed to the control system, if the automatic boiler is also operating at the same time, the system will go into link up.

Positioning the Dry Well Thermostat

 In order that the dry well thermostat carry out its purpose efficiently it is crucial that it is correctly sited and installed on or near the solid fuel appliance, see figures 7, 1A, 1B, & 1C below


Dry Well Thermostat fitted close to the boiler in the solid fuel flow pipe


Dry Well Thermostat fitted in solid fuel boiler unused flow pipe


Dry Well Thermostat Installation

Contents of the dry well thermostat box

dry well thermostat
 PVC grommet and alternative thermoplastic fixing for the wiring.

The dry well pocket has a 1/2 inch BSP male thread so I will need a female fitting to screw it into. 

To accommodate the dry well pocket into the solid fuel flow I am going to use a 28x15x28 tee, one end reduced, a standard 15mmx1/2 inch straight female connector and a short  piece of 15 mm pipe (length of the pipe will vary depending on what type and even brand of fitting you are using) .

I could have used a male connector and gone straight into the tee, but did not have one available

Introduce the pipe to the connector, and....

the pipe to the fitting.

Loosen the dry well pocket retaining screw and.....

Carefully slide the dry well pocket off the copper bulb sensing element. Please handle with care.

To ensure the thermostat is as responsive as possible it is important that the dry well pocket is right into the solid fuel flow, as in the diagram above. Before I start any soldering I check it is sitting correctly by......

sliding the dry well pocket into the fitting and...

screwing the dry well pocket into the 1/2 inch female connector. If the well is not right into the flow shorten the 15mm pipe until it is.

When pipe length is adjusted correctly, unscrew the dry well pocket and

flux and solder joints.

Wrap the 1/2 inch thread of the dry well pocket with sealing tape and screw into the female fitting

tighten with a spanner

Remove dry well thermostat thermoplastic cover retaining screw

remove thermoplastic cover

Terminals are clearly labelled, when temperature set is satisfied  the snap action microswitch makes terminals 1-4

1. Common (C)

2. Break on temperature rise (NC)

4 Make on temperature rise (NO)

Slide the wire through PVC grommet and connect two wires to terminals 1 and 4 earth wire and to earth terminal. Please note terminal 2 is not used.

Tighten terminal screws and slide grommet up

Slide grommet into thermoplastic cover and refit cover to thermostat

Carefully slide copper bulb sensing element into the dry well pocket

When thermostat is completely home tighten the dry well pocket retaining screw and.......

push the dial on.

Set dial to 58 degrees Celsius 

This end is complete.

Back to the H2 panel, remove Honeywell junction box cover

Terminals are labelled 1 to 10 from the left in this photo, it will be from top to bottom for you

a) connect earth wire to single loose earth terminal.

b) connect terminal 1 on the thermostat to terminal 1 on the H2 panel junction box and

c) connect terminal 4 on the thermostat to terminal 4 on the H2 panel junction box


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