Controlling pump with delay-off timer

[hollymcr]

I've recently moved into a house with a Greenstar 24Ri boiler, which (it transpires) hasn't been properly fitted. For the past 6 years, give or take, it hasn't had control of the pump (the fitter obviously decided it was too much like hard work to cable it back) and therefore the pump simply goes off when the room/tank stats stop calling for heat (or the programmer switches off). The boiler doesn't even have a permanent live; it either has power (in which case it's on and the pump is running), or it doesn't (and the boiler goes off and the pump stops).

The boiler however seems to be OK, although it has started kettling when the demand goes off and I'm sure the heat exchanger isn't "as new". I'm getting quotes to fix things properly.

However, in the meantime I have access to a delay-off timer, and I can't see any reason why it wouldn't be a better way of controlling the pump than I have at the moment without any major wiring work. Ie: the timer would take a maintained live and the switched live from the programmer (which currently controls the pump); the pump would be powered through the timer's relay which would come on when the switched live comes on, but would stay on for a period after it goes off.

Is there any good reason to avoid this temporary fix? If it's OK, how long should I set the timer for?

Just to be clear: I am not suggesting this as a long term solution. There are other issues (eg 15mm gas supply to the boiler) and I think the system could do with a flush (in which case I'd probably change the boiler at the same time). I just want to delay making major changes until spring/summer, and give the boiler an easier life in the meantime.

 

[MeldrewsMate]

I can't see any reason why not to, as long as you work safely with the electricity.

Indeed I have done similar to my father's system, but to make a by-pass radiator come on to warm his towels for 5 mins each morning, even if the DHW stat is satisfied....but then he has the pump correctly wired in to the boiler for over-run.

Suggest you only need 2 minutes to remove the heat soak from the boiler.

 

[hollymcr]

Thanks, it's installed and working.

I had someone out to quote for the corrective works and as he looked in the airing cupboard he saw the timer. I said he knew of a local housing estate where they'd had to deal with the same wiring issue across the whole estate and had used a similar solution, so that was another vote in favour.

I've also been advised to add X100 and X200 to the header tank. Any thoughts on that? Sounds like reasonable advice to me, but then I'm not a heating engineer!