Replaced pump and now have gremlins in my heating!

Hi all, I'm a new poster having read this excellent forum for advice for a while now. I've just replaced the pump on our heating system, and it's got going again but with a few issues Can anyone help please?

Problems are
1. 3 of the downstairs rads are stone cold (all upstairs and 2 others downstairs are fine). They were all working before.

2. Rads are heating up when hot water only is selected. It happens both when the heating temp control on the boiler is turned to off, and when the heating bit of the programmer is off, regardless. Don't know for sure if this was happening before the pump change or not, I hadn't noticed it but the heating was set to on a lot of the time anyway. Could be a red herring and not connected to what I've just done, but I'm not hugely competent at CH and am inclined to think the worst!

Info: system is an oil fired combi boiler (Worcester Heatslave), with inbuilt programmer, thermostatic valves on all rads but no separate room thermostat.

Not a pressure system (no expansion vessel) but a small tank in the roof with a ballcock to top up the heating and separate cold mains feed for hot water.

I've just replaced the pump with a Grundfos selectric 15/50, exactly the same as was fitted before, but (and this is a big but!) had a major argument with hubby over whether you can reverse said pump .... I don't know which bit you call which, but basically the replacement pump came with the flow arrow pointing the opposite way, but identical in every other way to the old model. The space for fitting it in the boiler is really tight, it's installed with the shaft horizontal and lying on top of the boiler just underneath the top cover, and there is no way it would go in the other way round. So I undid the allen nuts and flipped it around so the arrow now points the same way as the old pump when installed. He says it's fine to do that, I'm worried it can't be that easy.

I had read other posts on this forum warning that the isolating valves probably wouldn't work, and guess what - it was spot on! So it was a complete drain down, new valves fitted (which were longer, therefore had to cut the pipework down) and in with the new pump. Filled the system up yesterday and found a motorised valve which has to held open with a lever while refilling. I went and bled all the rads, and kept opening the pump screw to bleed that also. Finally tried it with heat, and now have hot water on demand, heat to some rads even when not demanded, and no heat to other rads no matter how nicely I ask

The pump appears to be working, the pipes on both sides of it are hot (the whole installation seems to be very hot though not boiling), and I'm getting heat to 75% of the rads. Those that aren't getting heat are stone cold, but they have been bled repeatedly and I'm sure it's not that. I've checked that the lockshield valves are all at least partially open and that the TRVs are all asking for heat.

I would be SO grateful for some friendly advice as I don't quite know what to do next. I'm not very technical, but have benefitted a lot this weekend from getting up close & personal with my boiler, so if anyone can suggest solutions I would really appreciate it. Sorry for the long post, I suspect I have more than 1 problem here!!

Thanks in advance

turn off all the rads which are heating and leaving the cold ones on, then run your heating with the pump at full speed and see if that brings them through. The other fault will be your motorized valve passing, gets very noticable when the hot days arrive. from cold run the system on hot water only annd check the heating pipe from the valve....if it warms up then its shot.

Provided the arrow is going the right way you can spin the head in any orientation by undoing the four (4) screws.

Yep easy as that.

Rads that don't work are probably air locked, you need to bleed them with one end turned off, then reverse the proccess.

Could try turning the ones that work off

Wow, impressive speed of replies - thanks so much both of you!

Doitall - really glad about the pump but does that mean I have to apologise to my husband? (gnashes teeth)

nickschicks said:

Wow, impressive speed of replies - thanks so much both of you!

Doitall - really glad about the pump but does that mean I have to apologise to my husband? (gnashes teeth)

Click to expand...

provided the arrow is the same way as the old one, yep

Could be TRV's stuck shut. SOmething in FAQs I think.

Brilliant advice on all counts, thank you so much.

Hubby now very smug, rads all warming up so with a little balancing we should have a working system.

Only problem I have now is with this valve - the rads have warmed up beautifully but with the control set to hot water only

Having felt the pipes coming from the valve, it seems to be giving equal priority to both CH and Hot Water, they both started to warm pretty much from go and are now both equally hot. So, a follow up question if I may - is there any easy way to find out if it's the electrical bit, the valve or both, and could it be something as simple as a sludged up valve that the motor is trying to close but can't? The electrical box does look pretty naff, quite corroded and a google search doesn't bring up any current versions of it (Appliance Components Motortrol), so I'm guessing it's probably pensionable age.

I have a silver box, sitting in front of a 3 way joint - one branch goes to the hot water 'jacket', the second goes into the bottom of the heat exchanger and the 3rd comes back in from the pipe marked 'central heating return' - can someone tell me in simple terms what I have to go shop for?

Thanks again
Anne