Central heating not switching on

[Malcolm Durnford]

Hi
We have an old gravity fed gas central heating boiler. The hot water works fine, but recently the heating failed to come on. I checked the thermostat which appeared to be sending the correct live signal to the junction box when the stat was turned up. The problem appeared to be with the synchron motor as when I pushed the lever to manual the central heating fired up.

I duly replaced the motor and initially the heating still did not come on. However, after a while it did and has been turning on fine for the last fortnight. However, the same problem has occurred again.

Is this likely to be a second failed synchron motor (can I test it?) or could some this else be causing the problem?

Many thanks
Malcolm

 

[ericmark]

There are Plans I think Honeywell invented them, C, Y, S, W etc, without knowing which hard to say, you say synchronous motor so assume your talking about a motorised valve? In the valves there are often V3 micro switch

which are well know for sticking and failing, the idea is a cam on valve operates switch as it opens so pump and boiler don't run if valve not open, with Y and C plans the DHW is default so that will often work even if valve not open.

Often one can renew valve head without the base, saves draining water, but must ensure valve is free to work. With the Y plan you have a three port valve, and if hot water called for it can cause the system to seem to work, even when the valve is faulty. To allow bleeding the system there is a manual lever on the valves, but with three port it only opens it half way.

Often one can work out if valve is open as lever goes slack and often there is an indicator, but Y plan have change over contacts in the DHW tank thermostat which if not working can stop central heating from working, also change over contacts in the programmer, so there are 4 items.
1) Programmer
2) Motorised valve
3) Tank Thermostat
4) Wall thermostat
Any one of these going faulty can stop central heating working with Y plan. So first what plan are you using, are there motorised valves and if so how many ports 2 or 3 and how many valves.

 

[Malcolm Durnford]

Hi
I must be honest, I am not sure which plan I have. There is only the one motorised valve

 

[terryplumb]

You have a Y plan system. Change the whole 3 port valve.

 

[Malcolm Durnford]

Will any Honeywell triple port valve be ok or are they model specific?

 

[terryplumb]

Wiring is industry standard on all ,as are port identity. Stick to Honeywell or Drayton, and steer clear of cheaper alternatives.

 

[Malcolm Durnford]

Thank you
I will purchase and fit over the weekend, so fingers crossed l