Friday, July 12, 2019

S-Plan, Y-Plan, Incompetence And Old Skool Protectionism

Marcus and Agata are about as far away from specialists in Heating systems as there can be, but our system in England has malfunctioned.  So we thought ...

How difficult could it be to fix it?

As Professional Engineers we hope to have some chance

The Malfunction
We use a computerised Heatmiser heating control system.  It has temperature sensors in rooms and an Internet Gateway add-on so we can monitor and adjust everything remotely.

However, we recently noticed that when the control system was switched off, somehow the Boiler was still turning on and heating up the Hot Water 24x7.  We just could not stop it!

How Uncovered

Although our home in England is just 2 years old, a combination of Legal and Engineering problems will soon force us to replace the heating.

As an interim we thought that we could economise by turning off the Central Heating, and during the summer months use only the Electrical Immersion heater backup element.

This would mean hot water only  (and so no heated towel rails or floors) but it is the summer right!

And it was only in the process of implementing that where we noticed that the Heatmiser was apparently not stopping.  In fact it was sort of a HeatHog not Heatmiser.  Maybe the issue has been intermittent for a while as we've had some absolutely huge heating bills in the last  year


In the process of trying to unravel how the base system works we came across what Marcus would term old skool protectionism.   I'd seen this in my profession with Mainframe computers in the 1970's.  People used to walk around smugly, being important.  They seemed to belong to a secret club, to which you were not invited, and they would not share their knowledge with you.  And any documentation you might uncover was convoluted, and missing detail.

And so I come to Heating systems design.

In the ordering of the   ESi ESCTDEB Dual Cylinder Thermostat  I found

- Very little description anywhere of how the Heating Systems work

- Incompetent workmanship:  Our Cylinder and Copper pipework actually block the installation of the Thermostat, so it can't be properly attached.  It's literally just hanging on as you can see from the stupid angle

- The ESi documentation is a mess.   No definition of terms.  Example  SPDT control,  HWS N/C  HWS N/O, S-Plan, Y-Plan

- No clear explanation of how to electrically connect up the Thermostat

Thankfully the walled garden is crumbling in 2019 and these two videos  were valuable

S Plan heating from JW (part of a series)

S Plan Heating and 2 Port Valves

Our S Plan Heating System

(And what is Y Plan)

After finding references to S-Plan and Y-Plan in the ESi installation guide I had to research what it was talking about.

Essentially a Y plan system uses a 3 way valve to direct the input hot water to the heating or hot water or both.

A S plan system uses a multi zone approach with each zone being controlled by a 2 way valve.   The input to each zone is the hot water from the boiler and then it goes thru the 2 way motorised valves to each zone.

At home we have an S plan system with 3 zones for Hot Water,  Underfloor Heating, Radiators

Legacy Design

I looked at the design of the system and concluded this must be some sort of legacy when devices had no computer control.   The system works on a  logical AND basis as shown above.

In our case the fault was that the Thermostat was in error. No matter what the input from Timer A it decided to always send a message to valve C as 'open and continue'.  So no matter the temperature of the boiler or the value of the Timer   (e.g. Off, don't do anything)  it ignored all of that and caused the heating to be continuously on until the safety cutout temperature was reached.

If I was designing a heating system in 2019 I'd use a CPU controller like an ESP32 NodeMCU as my central intelligence unit and have all the sensors feed into it, and then I'd control the output boiler.

I can imagine though that a whole industry has grown up using the CPU-less hard wired system shown first and so component manufacturers can't easily promote a new way of working that would be more reliable and appropriate for 2019.

Learning Points

- I now understand Heating systems just a little better.  There is some, but not much out there on the Internet including YouTube

- Seems like Heating systems are one of the last bastions of not very publicly documented design.   IMHO they keep it quiet so that people in the trade seem to be the only ones to easily fix your system, when actually, it is perhaps possible to fix it yourself.

I understand this position and mentality having grown up with protectionist 1970 Mainframe computer systems