Pressure Dirichlet value in BiCG STAB
 

I am solving the pressure poisson equation in BiCG STAB, I am using finite element formulation. the matrix is like this AX=B. Where A is the matrix where each row represents the weight of the surrounding nodes of that node considered(can be taken as the center node which is unknown). X is the unknown node phi and the corresponding B is the known value of the grad times the provisional velocity.
Suppose if there are 9 nodes in 2D, the nodes be numbered from 1 to 9, let 9th node be the center of all other nodes, then the matrix A the row will look like,
[weight of node1 weight of node2 .. .. .. .. .. .. .. weight of node 8]
the X will be
[phi of 9]
and B will be
[grad times velocity]

The problem is when we consider the pressure nodes with known values(i.e., Dirichlet nodes) , then i remove the weight of the nodes from A and add that to B with the given dirichlet values multiplied with the weights of that nodes.
This makes the solution to diverge when i give any values other than zero(dirichlet), Can anyone help me how to give this constant dirichlet value in the matrix??

Are you using a library or is your own-made solver?

its custom made solver, it works fine when pressure dirichlet value is given as zero, but when i give some numerical value it diverges, and the preconditioner is ILU for the solver

Check if your solver converges with a source term such that the solution is constant, for example 1