Failure of central heating hot water controls.

Postby Mauvern » Thu May 01, 2008 8:21 pm

I have a fully pumped two zone heating system which, until several days ago, was working fine with the heating and hotwater working independently of each other. Then the hotwater ceased to work at all, whilst the heating continued to operate fine.I checked the cyclinder thermostat (ACL brand) It was obviously very old and worn. I checked that power was reaching the thermostat and it was to each of the two leads connected to the thermostat, but the hotwater 2 port valve was not being activated by the stat. The valve concerned (Honeywell brand) was replaced professionally about two years ago, had given no trouble since then and cosmetically appears to be in good order. It can be manually operated and has a a position in which it can be kept open I have used this, in combination with the heating and its pump control, to obtain a minimal amount of hot water since the problem arose. I purchased and fitted a new thermostat (Honeywell 641) to the cyclinder, but it has'nt made a jot of difference, the hot water controls show no signs whatsover of being activated The hot water controls in the programmer appear to be switching their componets and connecting and disconnecting power as they should do. Any suggestions as to cause or advice as to possible solutions would be greatly appreciated. Thanks.
Posts: 2
Joined: Thu May 01, 2008 7:49 pm


Simply Build It

Postby ericmark » Fri May 02, 2008 9:13 am

Under the title "SUNDIAL PLANS DETAIL" Honeywell web site shows the different plans for wiring central heating. I think you will be on "S" plan. When testing at the cylinder thermostat you are only checking line maybe you have lost the neutral to valve? And what are you testing with neon screwdrivers for example can be really misleading. I use a clamp on Ammeter so I can see not only if line is getting to valve but also if it is drawing current. I have found although the plan may only show one micro switch often there are more which control the internal working of the valve as a result tests can be miss leading. Sorry can't really help much more locating what has gone wrong can be hard enough on site trying to sort remote is not likely to help much.

Postby Mauvern » Fri May 02, 2008 4:34 pm

Thanks for your reply, the interest taken and the info/advice given, I appreciate it. You are right, being an amatuer I used a neon screwdriver to check for power presence, being inexperienced I thought it was serving my purposes. I "saved" the wiring diagrams,etc from SUNDIAL PLANS DETAIL and my own system is undoubtedly similar. When we moved here some 7 years ago, a brand new boiler was installed as part of the deal. It follows that the central heating system must have been very old even then. It would seem that the original installation was to the specification of the ACL "Lifestyle" fully pumped twinzone layout. This appears to be confirmed by a basic use of ACL components, TVR's, room stat, cyclinder stat, motorised valves, ACL LWC1 wiring centre, etc. The previous owners had canibalised this by using other brands of small items to maintain the system.Inside the wiring centre is a printed stickon chart for the twinzone wiring layout. The installed wiring follows this very closely, utilizes the identical colours and carries tabs on each wire, showing their intended use, e.g., "Roomstat", Cylinder stat", "HW Valve", etc. The wiring loom is installed in a numbered connectior strip, some 16 capacity wide, with 15 of these being used. As already stated, for our first 5 years we had no problems, then the hot water facility became useless in a similar fashion to that currently experienced.A local heating concern diagnosed a faulty hot water motorised valve, changed the original ACL model for one made by Honeywell and departed. All seemed well until the present problem arose. I suppose it is possible that the the Honeywell valve has itself become defective, but I rather doubt this. I shall continue in my attempts to put matter right and your advice and info. will be a help in this.Thanks once4 again.
Posts: 2
Joined: Thu May 01, 2008 7:49 pm

Display posts from previous
Sort by
Order by


  • Related Topics