DIY Doctor UK DIY Forums

A recent problem turned up with my central heating.
It is a classical gas open vented system: gas boiler, loft cistern, indirect hot water cylinder, cylinder thermostat, living room thermostat, controller with separate knobs for hw and ch.

Symptoms:
1) if HW is off, nothing happens (irrespective of the thermostat setting and/or the CH switch)
2) if HW is on, both radiators and cylinder will be heated, but only until the cylinder thermostat is triggered
3) when 2 applies, the CH setting or living room thermostat have no influence on anything

I'm quite puzzled, because I cannot imagine of an explanation for this set of symptoms, given the fact that my system has two separate valves and a single pump (see pic).
Any suggestion on what could the problem be?



I also attach a pic of the controller/programmer (SANGAMO 410, Form No.: 1).
Further details of the components:
- grundfos 59506180 (pump, left on the pic)
- Honeywell v4043H1056 ( two-way control valve/diverter, bottom of the pic)
- bgmvsp-2 (two-way control valve/diverter/actuator, top of the pic)



Thanks in advance!
mbc

Micro switches in the motorised valve have likely failed. In my daughters we found latching the bleed lever to bleed position with Y plan got the heating working, however in the summer the radiators come on warm when the domestic hot water calls for heat.

So motorised valves allow you to swap just the head without touching the water bits.

To add to what I have already said, standard way central heating works is the thermostat operates the motorised valve, then the micro switches in the motorised valve work the boiler.

This means if the valve sticks the pump is not pushing against a closed valve, however the V3 micro switches used in the valves are not best quality and do fail, at around £1 each can't really expect them to work for ever.

However swapping a switch is no easy task, and buying them also unlikely to find them for sale on the high street, so in the main we swap either whole head or whole valve.

Testing is not easy, as other not only does the valve use V3 micro switches to control boiler, but also used to control valve, so often you find back feeds which can lead you astray.

Lucky the valve colour codes for wires do seem universal so.
Brown and Blue = Line and neutral to motor.
Gray = NO for micro switch normally permanent line.
White = NC for micro switch often not used some times connects to pump.
Orange = Com normally powers boiler and pump.

I have tried to work out what system you have, however top valve seems to be two port and bottom one three port which don't normally go together. If me I would feel around bottom valve for a leaver which works the valve and try manually opening the valve, it only actually opens the valve half way as designed to allow bleeding, and it can often be latched open, you may find that gets heating working on a temporary basis giving you time to get spares required.

Please say how you get on, it may help others.

Hi ericmark, I perused your thorough answer, which I'm grateful for!
Maybe it helped trying to make sense of what's happening.

ericmark wrote:I have tried to work out what system you have, however top valve seems to be two port and bottom one three port which don't normally go together.

I did some further research.
According to the official specs
http://www.honeywelluk.com/documents/Installation-Guide/pdf/1081.pdf,
that looks like a two port, but maybe I'm wrong?
[/quote]

ericmark wrote:If me I would feel around bottom valve for a leaver which works the valve and try manually opening the valve, it only actually opens the valve half way as designed to allow bleeding, and it can often be latched open, you may find that gets heating working on a temporary basis giving you time to get spares required.

Indeed, there is one lever, about which the specs say

I set it to "MAN OPEN", but that didn't have any noticeable effect.

ericmark wrote:Please say how you get on, it may help others.

What I can do is try to replace that valve, because replacing the micro switches looks a bit daunting!

Many thanks again, I'll report in case of progress :)