Central Heating not workign Hot water OK

We had this issue last year, but went away a day or so later. Anyway it happened a few weeks ago and I bleed all the rads and it seemed to fix it. But now it's packed up again. Here are the details.

Thermosat - Old Honeywell mechanical job (three wire)
Timer - Mechanical Danfoss 102
Boiler Baxi WM 381 RS C.H.B

Everything looks pretty old.

OK. First up, although the thermo is pretty crap it does seem to work. When it fire up it clicks and a switched circuit kicks in at 230v.
Timer seems to work as hot water works and switching it to hot water only, stops the 230v to the thermostat.
I've flushed the system and added sludge treatment. Left two weeks and drained the system several times. Pretty scummed up.

I worked out which pipe comes from the boiler to the heating (as opposed to the hot water tank) and bleed this as well, again pretty sludgy.

Now when hot water fire up all seems ok. The C.H pipe also gets hot. Bleeding this at the boiler and the water is hot, but the rads are stone cold.
If the hot water is not being heated, the flames do NOT come on.

I'm guessing there is a pump somewhere in the boiler, but can't see one and not being stupid I have no intention of removing the boiler covers..

Is it likely to be some sort of pump (would this stop the flame coming on), or another issue?

If it is a pump, do you thing they are available and if so what am I looking at?

Thanks for any guidance.

Stu..

yes you have a pump

no it's not in the boiler

easiest option is to follow the pipes

View media item 667
this is what you are looking for (might not be the colour)

go play hunt the pump

and its prob stuck

Thanks for your quick reply.

Am I likely to have 2?

I have found a similar one, but it seems to be conected to the hot water tank, with pipe half way up the cylinder. Then it goes to a "paddle direction indicator) and the branches of in two directions.

All my pipes are internal so not being easy to trace.

Stu.

Forgot to add, this seemed to be doing little so I cranked up the speed and it went nuts, loads of gushing water in the pipes, after 5 mins turned it back down, but still now hot water in rads.