Combi boiler problem - yes it's an Ideal Isar HE30....

[shambolic]

Sounds like hw thermistor fault and possibly pump. Hard to tell as your descriptions are all over the place.

 

[Bowerleigh24]

Hello all and thanks for your advice so far. I have another question:

I've had a replacement pump delivered which I'm about to attempt to fit. The manual says that, in addition to draining the system, I have to "Close all the water isolating (CH and DHW) valves on the piping frame." They are extremely stiff, and made from copper, so are also quite soft. I'm worried that if I try too hard I'm going to damage them so, my question is, do I really have to close the valves if I'm draining the circuit?

 

[Bowerleigh24]

Update and question (!):

Hello all

So I've had a week or so without heating or hot water and am about to run myself a nice hot bath!

I replaced the pump with a used/tested one from eBay (including manifold which I didn't use), (£50 inc postage). I now had hot water for a few seconds before the H3 error code appeared and, after a few switches back to 'D', shut the system down. Taking Shambolic's advice, I sent off for a DHW thermistor, which I've now fitted. I was a bit of a pain in the proverbial because the old one was not going to come out (it's a push fit with a clip). So I decided to remove the plate heat exchanger so I could push it out from the other side. Unfortunately the torx screws were in a bad state so I had to drill one out and cut a slot in the other to unscrew. I found some hex replacements at B&Q. While the plate heat exchanger was out I left descaler in to soak for a few hours and got some chunks of scale out.

So here's my question:

Touch wood I now have heating and hot water. I've got a couple of things still to do, eg add inhibitor, maybe bleed the pump, empty condensate trap etc, but more pressingly, I note the water pressure (hot AND cold) has dropped, well the flow anyway. I wonder if a loose piece of limescale is sitting in the heat exchanger and that's what's slowing the flow. However, I think it a bit odd that the flow is reduced for the cold water too - no limescale on that side of the PHx. Before I drain down and remove and pressure wash the PHx, I wondered if you folks have other suggestions as to possible causes!

Thanks