Delay timer in Central heating setup

conolan

In a 4 year old house, which had only 1 zone and simple timer. Got plumber to put in two motorised valves, close to where the boiler pipe comes into utility. Plumber never told me there should be a bypass. Currently when timer tells boiler to stop, valve closes and boiler stops firing. Pump keeps pumping to dissipate heat in boiler and has nowhere to go. Boiler thermostat pops due to excess heat.

Was going to get plumber back, then a thought occurred.

Could I put in a time-delay into the circuit before the valve, and another relay between valves and boiler. Thus when timer calls a halt, boiler stops but valve remains open for a few mins so pump can send hot water through house and dissipate residual heat.

See diagram here.

Will this work? Time delay relays will be these and relay before boiler will be normally open, closed when power is supplied.

Note: Receivers refer to wireless thermostat/controller system that sends signals to receivers to indicate when valves and boiler are to operate.

A good heating system is a basic heating system, if you design a system that unique to you then if ever you need any fault finding done plumbers will be running in the opposite direction, fit a bypass so that if ever your zone valves fail the boiler will not over heat, if you put in a time delay how do you know the delay will be sufficient to dissipate the heat, Gary

conolan

Fitting the bypass is problematic because there is little room for it. As for the time, I just have to work out how long the pump normally runs for and set my timer for a little longer. Don't I?

DublinDilbert

conolan wrote: »

Fitting the bypass is problematic because there is little room for it. As for the time, I just have to work out how long the pump normally runs for and set my timer for a little longer. Don't I?

Maybe you could also use the run-on signal to the pump to switch a relay to keep the valve powered up.... You'd probably need to introduce some logic, possibly a second relay but it probably could be made to work.....

And would mean that as long as the pump runs there'll be somewhere for the water to go. If we had a complete circuit diagram i'm sure we'd be able to figure out something....

If you keep the two port open after the room stat has stopped calling for heat, wont that impact on the effectiveness of the room stat i.e if you dump the heat down zone 1 and the pump is keeping the two port open and zone b takes longer to achieve temp you will then over cook zone 1.

I am not saying what you want to do with the timed delay is not going to work, but i would contact the technical department of the boiler manufactures for some input, as a boiler manufactures technician i wouldn't like the idea because if the two port fails the boiler will overheat, Gary.

youtheman

The 'pump over-run thermostat' keeps the pump running after the burner has been turned off (so that you can use the residual energy in the system).

I think fitting a bypass valve is the way to go. It's a lot simpler, cheaper, and will be more 'fail safe' than the extra wiring and solenoids. If your actuated valve fails closed then the system has no way of knowing that they are 'in fault'. The bypass valve will connect the supply and return, so the pressure won't build up. The system will eventually turn itself off when the water thermostat trips (the 'ultimate relief' as far as over-heating goes).